Montserrat Phone Numbers: Format, Area Code & Validation Guide

Learn how to call Montserrat using country code +1-664 and validate Montserrat phone numbers in your applications. This comprehensive guide covers the NANP phone number format, area code 664 dialing instructions, validation techniques, Mobile Number Portability (MNP), and implementation with libphonenumber-js for developers and telecom professionals.

Who should use this guide: Software engineers building contact forms, CRM systems, SMS platforms, or authentication services; telecom professionals managing number assignment; compliance teams ensuring proper number handling; and anyone needing reliable Montserrat phone number validation.

Common use cases: User registration and verification (OTP/2FA), international calling features, contact database validation, SMS delivery optimization, carrier routing, emergency service integration, and regulatory compliance for telecommunications applications.

Understanding Montserrat's Telecommunications System

Montserrat, a British Overseas Territory in the Caribbean, uses the North American Numbering Plan (NANP). This integration simplifies communication with other NANP regions while maintaining a unique identity through area code 664. Area code 664 was created in a split of area code 809 on July 1, 1996, following a permissive dialing period that ended June 1, 1997.

Market context: As of January 2025, Montserrat has a population of approximately 4,373 people (DataReportal Digital 2025). Despite this small population, 9,181 cellular mobile connections were active in early 2025 – equivalent to 210% of the total population – indicating that many residents maintain multiple mobile connections for personal and business use. Internet penetration stood at 55.9% (2,444 users) at the start of 2025. This high mobile connection density relative to population size creates unique challenges for number management and carrier competition strategies.

The Montserrat Info-Communications Authority (MICA) regulates the telecommunications sector. MICA was established on August 1, 2009, with responsibility for managing telecommunications licensing, spectrum allocation, and ensuring fair competitive practices among info-communications providers.

Current providers: Flow (operated by Cable & Wireless, the incumbent provider) and Digicel (launched in 2015) are the two main telecommunications operators. Both providers offer LTE services (launched 2017–2018) using 700 MHz spectrum. In September 2020, Montserrat connected to a new subsea fiber system, and in 2021 the government initiated a fiber-to-home project with both providers to ensure island-wide connectivity.

Montserrat Phone Number Format: NANP Structure Explained

Montserrat phone numbers adhere to the NANP structure:

This standardized format ensures compatibility within the NANP. Each component serves a specific purpose:

• +1: The country code for all NANP members, including the US, Canada, and parts of the Caribbean.
• 664: Montserrat's designated area code.
• XXX: The three-digit exchange code, also known as the Central Office Code. This code identifies a specific geographic area or service provider within Montserrat.
• XXXX: The four-digit subscriber number, unique to the individual line.

Number Format Variations

Specific prefixes and ranges distinguish different service types:

Important: Exchange code assignments change over time. For the most current exchange code ranges and assignments, consult MICA's official documentation at www.mica.ms.

Exchange code allocation: New exchange codes are typically allocated when existing ranges approach capacity or when introducing new services (e.g., mobile services, VoIP). In small markets like Montserrat, allocations happen infrequently – often years apart – due to the limited population. MICA manages these allocations through its frequency authorization process. Check MICA's numbering plan annually for updates, though major changes are rare given the stable population size.

How to Validate Montserrat Phone Numbers

Robust phone number validation is essential for any application handling Montserrat numbers. Basic regular expressions provide a starting point, but relying solely on them is insufficient due to number portability and formatting variations.

Business impact of validation failures:

• Failed SMS delivery: Invalid numbers cause delivery failures, wasting SMS credits (typically $0.02–$0.10 per message) and preventing critical notifications from reaching users
• User friction: Legitimate users blocked by overly strict validation abandon registration flows (industry average: 15–25% form abandonment due to validation errors)
• Data quality issues: Accepting invalid numbers pollutes contact databases, reducing campaign effectiveness and increasing bounce rates
• Compliance risks: Calling disconnected or wrong numbers violates TCPA, DNC, or local regulations, resulting in fines up to $43,792 per violation (U.S. TCPA)

Common validation pitfalls to avoid:

1. Format-only checking without existence verification: Regex validates structure but not if the number is assigned or active
2. Ignoring country codes: Assuming all inputs include +1 prefix; users often omit it when entering local numbers
3. Not handling extensions: Business numbers with extensions (e.g., ext. 123) fail simple digit-only validators
4. Hardcoded exchange codes: Using outdated exchange lists from 2011 documentation; new codes have been allocated since then
5. No input sanitization: Failing to remove spaces, dashes, parentheses before validation
6. Missing MNP support: Assuming carrier from prefix, which breaks when numbers port between Flow and Digicel
7. Insufficient error messages: Generic "invalid number" errors don't help users correct formatting mistakes
8. No rate limiting: Validation API abuse or excessive real-time lookups hitting third-party service limits

Regular Expressions (Basic)

These examples offer basic validation:

// Basic landline validation (Based on documented exchanges as of May 2011)
// Note: This is illustrative – exchange codes have likely expanded since 2011
const landlineRegex = /^\+1-664-(236|349|410|411|412|413|415|664|724)-\d{4}$/;

// Mobile number validation (49X prefix – confirmed active: 491-496)
const mobileRegex = /^\+1-664-49[0-9]-\d{4}$/;

// Toll-free validation (includes all current NANP toll-free prefixes)
const tollFreeRegex = /^\+1-(800|833|844|855|866|877|888)-\d{3}-\d{4}$/;

Caveat: These regex examples are simplified and based on May 2011 exchange code assignments, which have changed. They are suitable for basic checks but not recommended for production environments without verification of current assignments.

Edge cases and invalid number examples for testing:

// Invalid examples – should FAIL validation
'+1 664 111 1111'  // Invalid exchange code (111 not assigned)
'+16649'           // Too short (incomplete number)
'+1 664 491 23456' // Too long (extra digit)
'664-491-2345'     // Missing country code
'+44 664 491 2345' // Wrong country code (UK instead of NANP)
'+1-664-000-0000'  // Reserved/unassigned pattern
'(664) 491-2345'   // Missing NANP country code +1

// Valid examples – should PASS validation
'+1 664 491 2345'  // Standard international format
'16644912345'      // E.164 format without separators
'+1 (664) 491-2345' // Common U.S. formatting style
'1-664-491-2345'   // Alternative hyphen format

// Ambiguous cases requiring context
'4912345'          // Valid IF default country is Montserrat
'664-491-2345'     // Valid IF calling from within NANP region

Best Validation Method: Using libphonenumber-js

For comprehensive validation, use a specialized library like libphonenumber-js (current version 1.12.24 as of January 2025, actively maintained with regular updates from Google's libphonenumber library). This library handles international formats, number portability, and other complexities, ensuring greater accuracy.

Installation and package size considerations:

npm install libphonenumber-js

Package sizes:

• Minified: 183.1 kB
• Minified + Gzip: 43.8 kB (typical over-the-wire size)
• Default metadata (/min): ~80 kB (basic length validation)
• Full metadata (/max): ~145 kB (includes precise regex validation and .getType() support)
• Mobile metadata (/mobile): ~95 kB (mobile-only validation)

Tree-shaking support: libphonenumber-js supports ES6 tree-shaking when using modern bundlers (Webpack 4+, Rollup, Vite). Import only the functions you need from /core with custom metadata to minimize bundle size. For projects requiring minimal footprint, use /mobile metadata if validating only mobile numbers, or generate custom metadata including only required countries.

Prerequisites: Node.js 12+ or modern browsers with ES6 support. TypeScript definitions are included.

import parsePhoneNumberFromString from 'libphonenumber-js'

const phoneNumber = parsePhoneNumberFromString('+16644911234', 'MS') // 'MS' is the ISO 3166-1 alpha-2 code for Montserrat

if (phoneNumber && phoneNumber.isValid()) {
  console.log('Valid Montserrat phone number')
  console.log(phoneNumber.formatInternational()) // Output: +1 664 491 1234
} else {
  console.log('Invalid phone number')
}

Enhanced code example with error handling, sanitization, and additional methods:

import parsePhoneNumberFromString from 'libphonenumber-js'

/**
 * Validates and formats a Montserrat phone number with comprehensive error handling
 * @param {string} input - User input (may contain spaces, dashes, parentheses)
 * @param {string} defaultCountry - Default country code (e.g., 'MS' for Montserrat)
 * @returns {object} Validation result with formatted number or error details
 */
function validateMontserratNumber(input, defaultCountry = 'MS') {
  try {
    // Sanitize input: remove common non-digit characters except '+'
    const sanitized = input.trim()

    // Parse with default country context
    const phoneNumber = parsePhoneNumberFromString(sanitized, defaultCountry)

    if (!phoneNumber) {
      return {
        valid: false,
        error: 'NOT_A_NUMBER',
        message: 'Input does not contain a valid phone number'
      }
    }

    // Validate the parsed number
    if (!phoneNumber.isValid()) {
      return {
        valid: false,
        error: 'INVALID_NUMBER',
        message: 'Phone number format is invalid or number does not exist',
        parsed: {
          country: phoneNumber.country,
          nationalNumber: phoneNumber.nationalNumber
        }
      }
    }

    // Extract detailed information
    return {
      valid: true,
      number: phoneNumber.number,               // E.164 format: '+16644911234'
      country: phoneNumber.country,             // 'MS'
      nationalNumber: phoneNumber.nationalNumber, // '6644911234'
      type: phoneNumber.getType(),              // 'MOBILE', 'FIXED_LINE', etc. (requires /max metadata)
      formatted: {
        international: phoneNumber.formatInternational(), // '+1 664 491 1234'
        national: phoneNumber.formatNational(),          // '(664) 491-1234'
        e164: phoneNumber.format('E.164'),              // '+16644911234'
        rfc3966: phoneNumber.format('RFC3966')          // 'tel:+16644911234'
      },
      isPossible: phoneNumber.isPossible(),     // Length check only
      isValid: phoneNumber.isValid()            // Full validation including digit patterns
    }
  } catch (error) {
    return {
      valid: false,
      error: error.message,
      message: `Validation error: ${error.message}`
    }
  }
}

// Usage examples
console.log(validateMontserratNumber('+1 664 491 2345'))
// Returns: { valid: true, number: '+16644912345', country: 'MS', ... }

console.log(validateMontserratNumber('664-491-2345', 'MS'))
// Returns: { valid: true, ...formatted versions... }

console.log(validateMontserratNumber('123', 'MS'))
// Returns: { valid: false, error: 'TOO_SHORT', ... }

// Additional utility methods
const phoneNumber = parsePhoneNumberFromString('+16644911234', 'MS')
phoneNumber.getCountry()                      // 'MS'
phoneNumber.getType()                         // 'MOBILE' (if using /max metadata)
phoneNumber.getPossibleCountries()            // ['MS'] or ['US', 'CA', 'MS', ...] for ambiguous numbers
phoneNumber.isNonGeographic()                 // false (Montserrat numbers are geographic)
phoneNumber.getURI()                          // 'tel:+16644911234'

Real-world integration considerations:

• User input forms: Use AsYouType formatter for real-time formatting as users type
• Database storage: Always store in E.164 format (+16644911234) for consistency
• Display formatting: Use formatNational() for local context, formatInternational() for global
• API responses: Return both E.164 and formatted versions for flexibility
• Validation timing: Validate on blur or form submit, not on every keystroke (performance)
• Caching: Cache validation results for repeat checks of the same number

Mobile Number Portability in Montserrat (MNP)

Montserrat has implemented Mobile Number Portability (MNP), allowing users to switch carriers while retaining their phone number. While MNP was launched across the Eastern Caribbean Telecommunications Authority (ECTEL) member states on June 3, 2019, Montserrat is not an ECTEL member state. ECTEL's five member states are: Dominica, Grenada, St. Kitts and Nevis, Saint Lucia, and St. Vincent and the Grenadines (established by treaty on May 4, 2000).

Montserrat MNP implementation: Montserrat operates its own independent MNP system regulated by MICA. While the specific launch date for Montserrat's MNP is not publicly documented in the same manner as ECTEL member states, MNP has been implemented and allows users to switch between Flow and Digicel while keeping their phone numbers. For exact implementation dates, porting timelines, and procedures, contact MICA directly at www.mica.ms.

MNP impacts validation because the original carrier assignment (based on exchange code prefix) no longer definitively indicates the current provider. A number originally issued by Flow now operates on Digicel's network, and vice versa.

How to Handle MNP in Your Applications

To determine the current carrier for a Montserrat phone number, integrate with a carrier lookup service. For Montserrat-specific carrier information, consult:

• MICA (Montserrat Info-Communications Authority): The regulatory authority for Montserrat telecommunications at www.mica.ms
• Carrier APIs: Flow and Digicel offer carrier lookup APIs or services directly

Always prioritize official and up-to-date resources for carrier information. Confirm the specific implementation details and availability of carrier lookup databases with MICA or the telecommunications providers operating in Montserrat.

Carrier lookup integration example (conceptual):

import parsePhoneNumberFromString from 'libphonenumber-js'

/**
 * Determines current carrier for a Montserrat mobile number
 * Note: This is a conceptual example – actual implementation depends on available APIs
 */
async function getCarrierInfo(phoneNumber) {
  // First validate the number
  const parsed = parsePhoneNumberFromString(phoneNumber, 'MS')

  if (!parsed || !parsed.isValid()) {
    throw new Error('Invalid phone number')
  }

  // Approach 1: Direct carrier API (if available)
  // Most carriers provide REST APIs for authorized partners
  try {
    const response = await fetch('https://api.carrier-lookup.example/v1/lookup', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${process.env.CARRIER_API_KEY}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        phoneNumber: parsed.number, // E.164 format
        country: 'MS'
      })
    })

    if (!response.ok) {
      throw new Error(`API error: ${response.status}`)
    }

    const data = await response.json()
    return {
      carrier: data.carrier,           // 'Flow' or 'Digicel'
      networkType: data.networkType,   // 'mobile', 'fixed_line'
      isActive: data.isActive,         // true/false
      lastPortedDate: data.lastPortedDate // ISO date if ported
    }
  } catch (error) {
    console.error('Carrier lookup failed:', error)
    // Fall back to prefix-based estimation (unreliable with MNP)
    return getCarrierByPrefix(parsed)
  }
}

/**
 * Fallback: Estimate carrier by prefix (unreliable due to MNP)
 * Use only when real-time lookup is unavailable
 */
function getCarrierByPrefix(phoneNumber) {
  // This is unreliable after MNP implementation
  const prefix = phoneNumber.nationalNumber.substring(0, 3)

  return {
    carrier: 'Unknown (MNP active)',
    estimatedOriginalCarrier: prefix.startsWith('49') ? 'Likely mobile' : 'Likely landline',
    warning: 'This is an estimate only. Number has likely been ported.'
  }
}

// Usage
getCarrierInfo('+16644911234').then(info => {
  console.log('Carrier:', info.carrier)
  console.log('Network type:', info.networkType)
})

Authentication and API requirements:

• Most carrier lookup services require API keys obtained through business agreements
• Some services charge per lookup (typically $0.005–$0.01 per query)
• Rate limits vary by provider (common: 100–1,000 requests/minute)
• Authentication methods: Bearer tokens, API keys, OAuth 2.0

Fallback strategies when carrier lookup services are unavailable or rate-limited:

1. Prefix-based estimation (with warnings): Use historical prefix assignments as a best-guess, but clearly indicate uncertainty due to MNP
2. Cache carrier results: Store carrier info with timestamp; refresh periodically (e.g., every 30–90 days)
3. Batch lookups: Queue requests and process in batches during off-peak hours to stay within rate limits
4. Graceful degradation: Continue with validation without carrier info; provide generic error messages
5. User confirmation: Ask users to confirm their carrier if lookup fails
6. Local database with periodic updates: Maintain a local carrier database updated monthly from MICA or carrier sources

Montserrat Phone Number FAQs

How do I call a Montserrat phone number from the United States?

To call Montserrat from the United States, dial 1 (the long-distance access code) + 664 (Montserrat's area code) + the 7-digit local number. For example, to call +1 664 491 2345, dial 1-664-491-2345. Since both countries use the North American Numbering Plan (NANP), you don't need to dial the international prefix (011).

What is the country code for Montserrat?

Montserrat uses country code +1, which is shared by all North American Numbering Plan (NANP) members, including the United States, Canada, and many Caribbean nations. Montserrat is identified by its unique area code 664 within the NANP.

How can I tell if a Montserrat number is mobile or landline?

Mobile numbers in Montserrat typically use the 49X prefix (491, 492, 493, 494, 495, 496), while landline numbers use other exchange codes like 236, 349, 410-413, 415, 664, and 724. However, mobile and landline numbers are intermixed in Montserrat's system, and Mobile Number Portability (MNP) means numbers switch carriers, making prefix-based identification unreliable. Use a carrier lookup service or libphonenumber-js with /max metadata for accurate number type identification via the .getType() method.

What are the emergency numbers in Montserrat?

Reach emergency services in Montserrat at 911 (police, fire) or 999 (police only). Ambulance services use +1 664 491 2802 or +1 664 491 2552. For non-emergency police matters, contact headquarters at +1 664 491 2555/2556. Emergency numbers do not require the country or area code when dialing from within Montserrat.

When was Mobile Number Portability implemented in Montserrat?

While Mobile Number Portability (MNP) was launched across ECTEL member states on June 3, 2019, Montserrat is not an ECTEL member state. Montserrat has implemented its own independent MNP system regulated by MICA, allowing users to switch between Flow and Digicel while keeping their phone numbers. For specific implementation dates, porting timelines, and procedures, contact MICA (Montserrat Info-Communications Authority) at www.mica.ms.

Which telecommunications providers operate in Montserrat?

Flow (operated by Cable & Wireless) and Digicel are the two main telecommunications providers in Montserrat. Flow is the incumbent provider with broader coverage, while Digicel entered the market in 2015 to provide competition. Both carriers offer LTE services using 700 MHz spectrum and are connected to a subsea fiber system deployed in September 2020.

What is the best library for validating Montserrat phone numbers?

The recommended library is libphonenumber-js (version 1.12.24 as of January 2025), a JavaScript implementation of Google's libphonenumber library. It provides comprehensive validation for international phone numbers, including Montserrat numbers, and handles formatting, number type detection, and other complexities. Use the ISO 3166-1 alpha-2 code 'MS' when validating Montserrat numbers.

How do I format a Montserrat phone number in international format?

Format Montserrat phone numbers in E.164 international format as +1 664 XXX XXXX (e.g., +1 664 491 2345). This format includes the country code (+1), area code (664), 3-digit exchange code, and 4-digit subscriber number. For local dialing within Montserrat, use the 7-digit format (XXX-XXXX). For calls from other NANP countries, dial 1-664-XXX-XXXX.

Are Montserrat phone numbers part of the Caribbean numbering system?

Yes, Montserrat phone numbers are part of the North American Numbering Plan (NANP), which includes many Caribbean nations. Montserrat received area code 664 on July 1, 1996, when it split from the original Caribbean area code 809. This integration allows seamless calling between Montserrat and other NANP regions using standard long-distance dialing procedures.

Best Practices

• Consult official documentation: Refer to MICA's official numbering plan document for the most accurate and up-to-date information.
• Use specialized libraries: Leverage libraries like libphonenumber-js for robust validation and formatting.
• Handle number portability: Implement carrier lookup mechanisms to account for MNP.
• Design for internationalization: Build your applications to handle international number formats.
• Test thoroughly: Test your implementation with various valid and invalid numbers.

Security considerations:

• Input sanitization: Always sanitize user input before validation; strip HTML, JavaScript, SQL injection attempts
• Rate limiting: Implement rate limits on validation endpoints to prevent abuse (recommended: 10–20 requests/minute per IP)
• API key protection: Store carrier lookup API keys in environment variables, never in source code
• Data encryption: Encrypt phone numbers in transit (HTTPS/TLS 1.3) and at rest (AES-256)
• Access logging: Log validation attempts with timestamps and IP addresses for security auditing
• PII compliance: Treat phone numbers as Personally Identifiable Information (PII) under GDPR, CCPA

Caching strategies:

• Validation results cache: Cache isValid() results for 24–48 hours (TTL) using Redis or in-memory cache
• Carrier lookup cache: Cache carrier info for 30–90 days; carriers rarely change frequently
• Formatted numbers cache: Cache formatted outputs (formatInternational(), formatNational()) to reduce CPU usage
• Cache key format: Use E.164 format as cache key for consistency: phone:validation:+16644911234

Compliance requirements:

• Do Not Call (DNC) lists: Check against national/regional DNC registries before initiating calls (U.S. TCPA, Canada CRTC)
• Consent management: Obtain explicit opt-in consent before sending SMS or making marketing calls
• Data retention: Follow local data protection laws for phone number storage duration (GDPR: delete when no longer needed)
• Right to erasure: Implement processes to delete phone numbers upon user request
• Cross-border transfers: Ensure compliance when transferring phone data internationally (GDPR Article 44–50)

Conclusion

Implementing Montserrat phone number validation requires understanding the NANP structure, area code 664 specifics, and Mobile Number Portability implications. Use specialized libraries like libphonenumber-js for production environments rather than relying solely on regular expressions.

Key takeaways:

• Montserrat uses NANP format: +1 664 XXX XXXX (country code +1, area code 664, 7-digit local number)
• Population: ~4,373 (Jan 2025); Mobile connections: 9,181 (210% penetration indicating multiple SIMs per person)
• Mobile numbers use 49X prefixes (491–496), but MNP means carrier identification by prefix is unreliable
• Emergency services: 911 or 999 (police), 911 (fire), +1 664 491 2802/2552 (ambulance)
• Flow and Digicel are the two main carriers, both offering LTE on 700 MHz spectrum
• Exchange codes documented in May 2011 include 236, 349, 410–413, 415, 664, 724, and 49X series
• Use libphonenumber-js version 1.12.24 or later with ISO code 'MS' for robust validation
• Package size: 43.8 kB gzipped; supports tree-shaking for minimal bundles
• MICA (established August 1, 2009) regulates telecommunications at www.mica.ms
• MNP is active in Montserrat (independent system, not part of ECTEL which launched June 3, 2019)

Next steps:

1. Install libphonenumber-js in your project: npm install libphonenumber-js
2. Review MICA's official documentation for current exchange code assignments
3. Implement carrier lookup integration if you need to determine the current provider
4. Test your validation logic with various Montserrat number formats (international, national, local)
5. Configure your application to handle both 911 and 999 emergency number formats
6. Test edge cases: Include tests for invalid numbers (+1 664 111 1111), short numbers (664-49), numbers with extensions (664-491-2345 ext. 123)
7. Set up monitoring: Track validation success rates, API response times, and cache hit ratios
8. Sanitize user input: Implement input cleaning to remove spaces, dashes, parentheses before validation
9. Implement error handling: Provide clear, actionable error messages for different validation failure scenarios
10. Audit security: Review rate limiting, API key management, and PII handling procedures

Related topics:

• NANP (North American Numbering Plan) structure and member countries
• E.164 international phone number format standards
• Caribbean telecommunications regulatory frameworks (ECTEL vs. independent authorities)
• Mobile Number Portability implementation best practices
• Phone number validation libraries comparison (libphonenumber-js vs. google-libphonenumber)
• MICA telecommunications regulations and licensing requirements
• International dialing codes and access prefixes by region