Northern Mariana Islands Phone Numbers: Format, Area Code & Validation Guide

Introduction

Area code 670 is the telephone area code for the Northern Mariana Islands (CNMI) in the North American Numbering Plan (NANP). Build applications that handle 670 phone numbers correctly with this comprehensive guide covering formatting, validation, E911 requirements, and carrier integration. Master CNMI telecommunications and build robust, reliable applications.

Area Code 670 Quick Reference

This table summarizes key information about Northern Mariana Islands (CNMI) phone numbers with area code 670:

Area Code 670 Background and History

Area code 670 serves the Northern Mariana Islands (CNMI) as part of the North American Numbering Plan (NANP). The CNMI shares country code +1 with the United States, Canada, and several Caribbean nations. The NANP system, established in the 1940s, simplifies dialing and enables direct international calls within the region. The plan introduced interchangeable area codes in 1995 and increasingly uses overlay plans to manage numbering resources efficiently.

When Was Area Code 670 Assigned? The Northern Mariana Islands received area code 670 in January 1997, when it joined the NANP along with Guam (area code 671). Before 1997, callers reached CNMI via international direct distance dialing (IDDD) using country code 670. The integration into NANP simplified calling between CNMI and the mainland United States by eliminating international dialing requirements (NANPA Planning Letter PL-038, January 1997).

The CNMI exclusively uses area code 670 – a critical detail for validating and processing phone numbers from this region. The telecommunications market includes two primary carriers: IT&E and DOCOMO Pacific, which provide services across the main islands of Saipan, Tinian, and Rota.

670 Area Code Number Format and Structure

Understanding the structure of area code 670 phone numbers is fundamental to processing Northern Mariana Islands numbers correctly.

Core Number Components

A complete CNMI phone number consists of these elements:

+1 670 NXX XXXX
│  │   │   └──── Subscriber Number (4 digits)
│  │   └──────── Exchange Code (3 digits)
│  └──────────── Area Code (670)
└──────────────── Country Code (+1)

• Country Code (+1): Identifies the NANP region.
• Area Code (670): Specifies the CNMI.
• Exchange Code (NXX): Represents a specific central office or exchange within the CNMI. The NXX cannot start with 0 or 1, and certain N11 combinations are reserved for special services.
• Subscriber Number (XXXX): The unique identifier for the individual subscriber.

Reserved N11 Codes: These N11 codes are reserved for special services and cannot be used as exchange codes (NANPA Abbreviated Codes):

The 3-digit code 988 serves as the National Suicide and Crisis Lifeline.

How to Format 670 Area Code Phone Numbers

You will encounter Northern Mariana Islands (area code 670) phone numbers in various formats:

• International Format: +1-670-123-4567
• National Format: 1-670-123-4567
• Local Format: 670-123-4567
• Variations with Punctuation: (670) 123-4567, 670.123.4567

Your application must handle these variations seamlessly. Here's a format normalization function:

import re

def normalize_mp_number(phone_number):
    """
    Normalizes a Northern Mariana Islands phone number to E.164 format.

    Args:
        phone_number (str): The phone number to normalize.

    Returns:
        str: Normalized number in E.164 format (+16701234567) or None if invalid.
    """
    # Remove all non-numeric characters
    cleaned = re.sub(r'\D', '', phone_number)

    # Remove leading 1 if present (11 digits total)
    if len(cleaned) == 11 and cleaned.startswith('1'):
        cleaned = cleaned[1:]

    # Verify it's a valid 10-digit number starting with 670
    if len(cleaned) == 10 and cleaned.startswith('670'):
        return '+1' + cleaned

    return None

# Example usage
formats = [
    "+1 670 234 5678",
    "(670) 123-4567",
    "1-670-555-0100",
    "670.987.6543"
]

for fmt in formats:
    print(f"{fmt:20} → {normalize_mp_number(fmt)}")

How to Validate Area Code 670 Phone Numbers

Validate Northern Mariana Islands phone numbers to ensure data integrity and prevent errors. Here's a robust Python validation example for 670 area code numbers:

import re

def validate_mp_number(phone_number):
    """
    Validates a Northern Mariana Islands phone number.

    Args:
        phone_number (str): The phone number to validate.

    Returns:
        bool: True if the number is valid, False otherwise.
    """
    cleaned = re.sub(r'\D', '', phone_number)  # Remove non-numeric characters
    pattern = r'^1?670[2-9]\d{6}$' # Matches +1 or 1 optional, area code 670, exchange 2-9, and 6 digits
    return bool(re.match(pattern, cleaned))

# Test cases
numbers = [
    "+1 670 234 5678",  # Valid
    "16702345678",      # Valid
    "670-234-5678",     # Valid
    "6701111111",       # Invalid (N11 special service - 111)
    "1 670 123 4567",   # Invalid (Exchange starts with 1)
    "+1 671 123 4567"   # Invalid (Wrong area code - Guam)
]

for number in numbers:
    is_valid = validate_mp_number(number)
    print(f"'{number}' is valid: {is_valid}")

Note on line 153 test case: The number "1 670 123 4567" is invalid because the exchange code (123) starts with 1, which violates NANP rules. Exchange codes (NXX) must start with digits 2–9, never 0 or 1.

This validation function handles various formats, checks for valid exchange code ranges (2–9), and excludes reserved N11 combinations. Add further checks based on your requirements, such as carrier-specific validation or blacklist checking.

911 Emergency Services in Area Code 670 (E911 Implementation)

Handle emergency calls in the Northern Mariana Islands with special consideration. Area code 670 uses Enhanced 911 (E911), which provides location information to emergency responders. The FCC mandates dispatchable location information with 911 calls – including building, floor, and room number where technically feasible (as required by RAY BAUM's Act, implemented August 2019, with compliance deadlines January 6, 2021, for fixed devices and January 6, 2022, for non-fixed devices).

Dispatchable Location Requirements:

• Fixed devices: Must provide automated dispatchable location (street address plus room/floor/suite)
• Non-fixed devices: Must provide automated dispatchable location if technically feasible; otherwise provide coordinate-based alternative location sufficient to identify civic address and approximate in-building location, including floor level in large buildings
• Technical feasibility: Determined by whether location can be obtained from available technology at reasonable cost without requiring hardware/software improvements (FCC 47 CFR § 9.16)

// Emergency call handling example with dispatchable location
function handleEmergencyCall(phoneNumber, deviceType = 'fixed') {
  const EMERGENCY_NUMBERS = ['911', '112']; // Include common emergency numbers

  if (EMERGENCY_NUMBERS.includes(phoneNumber)) {
    // Priority routing and data collection
    return {
      priority: 'HIGH',
      route: 'EMERGENCY_PSAP',
      location: getDispatchableLocation(deviceType), // Get required location format
      timestamp: new Date().toISOString(),
      callbackNumber: getOriginatingNumber(), // Include originating number for callbacks
      mltsNotification: sendMLTSNotification() // Kari's Law requirement
    };
  }
  // Handle non-emergency numbers
  return { priority: 'NORMAL' };
}

// Function to obtain dispatchable location based on device type
async function getDispatchableLocation(deviceType) {
    try {
        if (deviceType === 'fixed') {
            // Fixed devices: return registered dispatchable location
            return {
                type: 'dispatchable',
                streetAddress: '123 Main Street',
                building: 'Building A',
                floor: '5',
                room: '502',
                city: 'Saipan',
                state: 'MP',
                zipCode: '96950'
            };
        } else {
            // Non-fixed devices: attempt automated dispatchable location
            const position = await navigator.geolocation.getCurrentPosition();

            // Try to reverse geocode to dispatchable address
            const address = await reverseGeocode(position.coords);

            if (address && address.isDispatchable) {
                return {
                    type: 'dispatchable',
                    streetAddress: address.street,
                    building: address.building,
                    floor: address.floor,
                    city: address.city,
                    state: 'MP',
                    zipCode: address.zip
                };
            } else {
                // Fall back to coordinate-based alternative location
                return {
                    type: 'alternative',
                    latitude: position.coords.latitude,
                    longitude: position.coords.longitude,
                    uncertainty: position.coords.accuracy,
                    civicAddress: address?.approximateAddress || 'Unknown',
                    floor: estimateFloor(position.coords.altitude)
                };
            }
        }
    } catch (error) {
        console.error('Location retrieval failed:', error);
        // Prompt user for manual location entry as last resort
        return {
            type: 'manual_required',
            error: error.message
        };
    }
}

// Kari's Law: Notification to central location
function sendMLTSNotification() {
    const notification = {
        timestamp: new Date().toISOString(),
        event: '911_CALL_INITIATED',
        callbackNumber: getOriginatingNumber(),
        location: getCurrentRegisteredLocation()
    };

    // Send to security desk, facility management, or designated contact
    notifyCentralLocation(notification);

    return {
        sent: true,
        recipient: 'security-desk@facility.example.com'
    };
}

This example prioritizes emergency calls, routes them to the appropriate Public Safety Answering Point (PSAP), and collects crucial location data. Implement error handling for location retrieval failures with fallback mechanisms, such as prompting users for their location if automatic retrieval fails. Ensure your implementation complies with Kari's Law (implemented August 2019, effective February 16, 2020), which mandates direct 911 dialing without prefixes and requires notification to a central location within the facility upon a 911 call (FCC MLTS 911 Requirements).

Technical Implementation for Area Code 670

Integrate Northern Mariana Islands (670 area code) phone numbers into your systems with these practical guidelines.

Number Allocation Rules

Follow these rules when managing CNMI phone numbers:

1. Area Code Validation: Always verify that the area code is 670.

   python

   def is_valid_area_code(number):
       return number.startswith('670')
   

2. Exchange Code Requirements:

   • Must start with digits 2–9.
   • Cannot use N11 combinations (reserved for special services).
   • Must follow NANPA guidelines for number conservation. Avoid wasteful allocation practices and participate in number pooling initiatives where applicable.

Number Pooling and Conservation: Thousands-block number pooling allocates telephone numbers in blocks of 1,000 consecutive numbers (e.g., 670-234-5XXX) rather than entire 10,000-number blocks. This reduces wasted numbers in areas with multiple service providers. Wasteful allocation includes obtaining number blocks without demonstrable need, failing to utilize at least 75% of assigned blocks before requesting additional numbers, or holding unused inventory that you could return to the available pool (47 CFR § 52.20).

Carrier Integration for Area Code 670

For telecom operators working with area code 670 numbers, implement these essential features:

// Carrier routing example with Local Number Portability (LNP) support
const carrierRoutes = {
  'ITE': {
    ranges: ['670-2', '670-3'], // Example ranges - consult LERG database for actual assignments
    routing: 'SIP_TRUNK_1'
  },
  'DOCOMO': {
    ranges: ['670-4', '670-5'], // Example ranges - consult LERG database for actual assignments
    routing: 'SIP_TRUNK_2'
  }
};

// Determine carrier based on phone number using LNP database query
function determineCarrier(phoneNumber) {
    // In production, query the Local Exchange Routing Guide (LERG) or
    // Number Portability Administration Center (NPAC) database for current assignment
    const npacResult = queryNPACDatabase(phoneNumber);

    if (npacResult && npacResult.carrier) {
        return npacResult.carrier;
    }

    // Fallback to range-based lookup if LNP query fails
    const prefix = phoneNumber.substring(0, 5); // 670-X format
    for (const [carrier, config] of Object.entries(carrierRoutes)) {
        if (config.ranges.some(range => prefix.startsWith(range))) {
            return carrier;
        }
    }

    return null;
}

// Check if number falls within carrier's assigned ranges
function isInCarrierRange(phoneNumber, ranges) {
    const prefix = phoneNumber.substring(0, 5);
    return ranges.some(range => prefix.startsWith(range));
}

// Function to determine routing based on carrier and number range
function getCarrierRoute(phoneNumber) {
    const carrier = determineCarrier(phoneNumber);

    if (carrier && carrierRoutes[carrier]) {
        if (isInCarrierRange(phoneNumber, carrierRoutes[carrier].ranges)) {
            return carrierRoutes[carrier].routing;
        }
    }

    return 'DEFAULT_ROUTE'; // Fallback route
}

Obtain Carrier Assignments: For authoritative carrier number range assignments, consult the Local Exchange Routing Guide (LERG) maintained by Telcordia/iconectiv, or query the NPAC database for real-time Local Number Portability (LNP) information. The LERG provides the definitive source for central office code assignments and routing information.

Warning: Always implement fallback routing mechanisms for carrier network failures to ensure continuous service availability. Implement monitoring and alerting systems to proactively detect and address carrier outages.

// Circuit breaker pattern for carrier failover
class CarrierCircuitBreaker {
    constructor(carrier, threshold = 5, timeout = 60000) {
        this.carrier = carrier;
        this.failureCount = 0;
        this.threshold = threshold;
        this.timeout = timeout;
        this.state = 'CLOSED'; // CLOSED, OPEN, HALF_OPEN
        this.nextAttempt = null;
    }

    async call(routingFunction) {
        if (this.state === 'OPEN') {
            if (Date.now() < this.nextAttempt) {
                throw new Error(`Circuit breaker OPEN for ${this.carrier}`);
            }
            this.state = 'HALF_OPEN';
        }

        try {
            const result = await routingFunction();
            this.onSuccess();
            return result;
        } catch (error) {
            this.onFailure();
            throw error;
        }
    }

    onSuccess() {
        this.failureCount = 0;
        this.state = 'CLOSED';
    }

    onFailure() {
        this.failureCount++;
        if (this.failureCount >= this.threshold) {
            this.state = 'OPEN';
            this.nextAttempt = Date.now() + this.timeout;
            console.error(`Circuit breaker opened for ${this.carrier}`);
        }
    }
}

Number Portability Implementation

Number portability allows subscribers to keep their numbers when switching carriers. This requires careful coordination between carriers and the Number Portability Administration Center (NPAC).

sequenceDiagram
    participant Donor as Donor Carrier
    participant NPAC as Number Portability DB
    participant Recipient as Recipient Carrier

    Recipient->>NPAC: Submit Port Request
    NPAC->>Donor: Validate Request
    Donor-->>NPAC: Confirm Eligibility
    NPAC->>Recipient: Schedule Port
    NPAC->>All Carriers: Update Routing Tables

Port Completion Timelines: Under FCC regulations, simple ports (single-line residential/business) must complete within one business day of receiving a valid port request. Complex ports (involving multiple lines or special services) typically complete within 3–5 business days. Issue port rejections within 24 hours with specific reason codes.

Account for potential delays and complexities with number porting when designing your application. Implement retry mechanisms and status checking:

import time
from enum import Enum

class PortStatus(Enum):
    PENDING = "pending"
    PROCESSING = "processing"
    COMPLETE = "complete"
    REJECTED = "rejected"
    CANCELLED = "cancelled"

def check_port_status(port_request_id, max_retries=10, retry_interval=3600):
    """
    Check port request status with retry logic.

    Args:
        port_request_id: Unique identifier for port request
        max_retries: Maximum number of status checks
        retry_interval: Seconds between checks (default 1 hour)
    """
    for attempt in range(max_retries):
        status = query_npac_status(port_request_id)

        if status in [PortStatus.COMPLETE, PortStatus.REJECTED, PortStatus.CANCELLED]:
            return status

        if attempt < max_retries - 1:
            time.sleep(retry_interval)

    return PortStatus.PENDING  # Still processing after max attempts

Best Practices for Area Code 670 Phone Numbers

Follow these best practices when working with CNMI phone numbers.

Error Handling

Implement robust error handling for number management:

import logging
import re

def sanitize_number(number):
    """Remove all non-numeric characters except leading plus sign."""
    if number.startswith('+'):
        return '+' + re.sub(r'\D', '', number[1:])
    return re.sub(r'\D', '', number)

def format_for_storage(number):
    """Format validated number in E.164 format for database storage."""
    cleaned = re.sub(r'\D', '', number)
    if len(cleaned) == 11 and cleaned.startswith('1'):
        cleaned = cleaned[1:]
    if len(cleaned) == 10 and cleaned.startswith('670'):
        return '+1' + cleaned
    raise ValueError(f"Invalid CNMI number format: {number}")

def is_valid_mp_number(number):
    """Check if number matches CNMI pattern."""
    pattern = r'^1?670[2-9]\d{6}$'
    return bool(re.match(pattern, number))

def process_phone_number(number):
    try:
        # Basic sanitization
        cleaned = sanitize_number(number)

        # Validation
        if not is_valid_mp_number(cleaned):
            raise ValueError("Invalid MP number format")

        # Format for storage
        formatted = format_for_storage(cleaned)

        return formatted

    except Exception as e:
        logging.error(f"Number processing failed: {str(e)}")
        raise  # Re-raise the exception after logging

This example catches and logs errors during number processing. Implement specific error handling strategies based on your application's requirements, such as returning specific error codes or user-friendly messages.

Performance Optimization

Optimize performance with these strategies:

1. Caching: Cache frequently accessed number ranges and validation results.
2. Batch Processing: Implement batch processing for bulk operations, such as validating large lists of numbers.
3. Efficient Data Structures: Use efficient data structures for number lookups, such as hash tables or tries.
4. Database Indexing: Maintain indexes on area code and exchange code fields for rapid queries.

Note on Mobile vs. Landline: Unlike some countries, the CNMI does not use distinct mobile prefixes. Both landline and mobile numbers share the same 670 area code and exchange code ranges. To distinguish between line types, query carrier databases or the Number Portability Administration Center (NPAC), which maintains service type information.

These optimizations improve your application's performance when handling large volumes of phone numbers. Profile your code to identify performance bottlenecks and optimize accordingly.

Additional Considerations

Carrier Identification Code (CIC) Filing Requirements: Beginning in 2025, telecom operators assigned Carrier Identification Codes must submit an Annual CIC Report to NANPA between January 1 and March 31 for the preceding 12-month period ending December 31. Submit the report via the NANP Administration System (NAS) using the standardized Excel template.

CIC Codes: CICs are four-digit codes (format XXXX, where X is 0–9) assigned by NANPA to identify carriers and other entities for billing and routing calls over the public switched telephone network (PSTN). Report each CIC annually with the following information:

• CIC number and type (Feature Group B or D)
• CIC Assignee name
• IAC Code (ACNA) – the 3-character Interexchange Access Customer code
• Usage status (Y/N)
• Disconnection status (Y/N)

Failure to submit the annual report may result in CIC reclamation. NANPA treats CICs reported as "not in use" for two consecutive years as abandoned and subject to reclamation (NANPA CIC Annual Report User Guide, October 2024; JSI CIC Filing Guidelines).

For detailed implementation guidelines and updates, consult the NANPA Guidelines and FCC Regulations. These resources provide valuable information on numbering plan administration, regulatory requirements, and best practices.

Conclusion

You now have comprehensive knowledge of area code 670 and Northern Mariana Islands phone numbers – including formatting, validation, E911 integration, carrier integration, and best practices. Follow the guidelines and examples in this guide to build robust, reliable applications that handle CNMI phone numbers effectively. Stay updated on NANPA and FCC regulations to ensure ongoing compliance.

Frequently Asked Questions (FAQ)

What is the area code for Northern Mariana Islands?

The area code for the Northern Mariana Islands (CNMI) is 670. This is the only area code used in the CNMI, which is part of the North American Numbering Plan (NANP) and shares country code +1 with the United States, Canada, and several Caribbean nations.

How do I format a Northern Mariana Islands phone number?

Format CNMI phone numbers in international format as +1-670-XXX-XXXX, where 670 is the area code followed by a 7-digit local number. The local number consists of a 3-digit exchange code (starting with 2–9) and a 4-digit subscriber number. Common formats include +1-670-123-4567, 1-670-123-4567, or (670) 123-4567.

How do I validate a CNMI phone number in Python?

Use a regular expression pattern that matches the NANP structure: r'^1?670[2-9]\d{6}$'. This pattern validates the country code (optional 1), area code (670), exchange code starting with 2–9 (not 0, 1, or N11 combinations), and 6 remaining digits. Remove all non-numeric characters before validation using re.sub(r'\D', '', phone_number).

What are the E911 requirements for Northern Mariana Islands?

The CNMI uses Enhanced 911 (E911), which requires location information with emergency calls. Under RAY BAUM's Act (implemented August 2019), you must provide dispatchable location information – including building, floor, and room number where technically feasible. Compliance deadlines: January 6, 2021, for fixed devices; January 6, 2022, for non-fixed devices (if technically feasible, otherwise coordinate-based alternative location). Kari's Law (effective February 16, 2020) mandates direct 911 dialing without prefixes and requires notification to a central location within multi-line telephone systems (MLTS) upon a 911 call.

Can CNMI phone numbers start with 0 or 1?

No. The exchange code (the three digits after area code 670) cannot start with 0 or 1. Valid exchange codes start with digits 2–9. Additionally, N11 combinations (like 211, 311, 411, 511, 611, 711, 811, and 911) are reserved for special services such as directory assistance and emergency calls, and cannot be used for regular subscriber numbers.

What is number portability in the Northern Mariana Islands?

Number portability allows CNMI subscribers to keep their phone numbers when switching carriers. The process requires coordination between the donor carrier, recipient carrier, and the Number Portability Administration Center (NPAC). Simple ports (single-line) must complete within one business day; complex ports typically complete within 3–5 business days. When designing applications, account for potential delays during porting and implement retry mechanisms or status checking to handle port requests gracefully.

What carriers operate in the Northern Mariana Islands?

The CNMI telecommunications market includes two primary carriers: IT&E and DOCOMO Pacific. Each carrier receives specific number ranges within the 670 area code. Both carriers provide services across the main islands, including Saipan, Tinian, and Rota. When implementing carrier integration, query the Local Exchange Routing Guide (LERG) maintained by Telcordia/iconectiv or the NPAC database for authoritative carrier assignments, as numbers may be ported between carriers. Always include fallback mechanisms for carrier network failures.

What are the CIC filing requirements for CNMI telecom operators?

Beginning in 2025, telecom operators assigned Carrier Identification Codes (CICs) must submit an Annual CIC Report to the North American Numbering Plan Administration (NANPA) between January 1 and March 31 each year. The report covers the preceding 12-month period ending December 31 and must include: CIC number, CIC type (Feature Group B or D), CIC Assignee name, IAC Code (ACNA), usage status, and disconnection status. Submit reports electronically via the NANP Administration System (NAS) using the standardized Excel template. Comply with this requirement to avoid CIC reclamation. NANPA treats CICs reported as "not in use" for two consecutive years as abandoned.