Frequently Asked Questions
Use a registered short code or 10DLC long code with a reputable SMS API provider like Twilio, Sinch, MessageBird, or Plivo. Ensure compliance with TCPA and CAN-SPAM regulations by obtaining explicit consent before sending marketing messages and respecting quiet hours.
10DLC (10-digit long code) is the standard for Application-to-Person (A2P) messaging in the US. It requires registration with The Campaign Registry to improve deliverability and compliance. It's suitable for various use cases like two-factor authentication, customer service, and transactional alerts.
A2P 10DLC registration helps combat spam and fraud, improving message deliverability and trust. It provides carriers with sender information, allowing them to better filter unwanted messages and ensure legitimate traffic reaches consumers.
Use short codes for high-volume marketing campaigns and time-sensitive alerts due to their higher throughput. Use 10DLC long codes for lower-volume applications like two-factor authentication, customer service interactions, and transactional messages.
SMS to landlines is possible but not always reliable. Some carriers convert the message to a voice call, while others may not deliver it at all. Verify number types and consider filtering landlines from SMS campaigns.
Single SMS messages are limited to 160 GSM-7 characters or 70 UCS-2 characters (for special characters). Concatenated messages can contain up to 1600 characters before splitting into segments.
Comply with TCPA and CAN-SPAM by obtaining explicit written consent, honoring opt-out requests within 24 hours, respecting quiet hours (9 PM - 8 AM local time), and registering for A2P 10DLC when using long codes.
You must support STOP, UNSUBSCRIBE, CANCEL, END, QUIT for opt-out and HELP or INFO for program details. These keywords should function in both upper and lower case.
Carriers filter messages to block spam, prevent fraud, and protect consumers from unwanted content. Common triggers include prohibited content (SHAFT), suspicious URLs, excessive punctuation, and all-caps messages.
Obtain clear and conspicuous consent through affirmative action, such as checking a box or sending a keyword. Document and store consent details including timestamp, source, and opt-in method for compliance.
Keep messages concise, include a clear call-to-action, personalize content thoughtfully, maintain consistent brand voice, and always respect quiet hours and frequency limits. Thorough testing and monitoring are also recommended.
Concatenated SMS messages in the US can contain up to 1600 characters before being split into segments. Each segment is limited to 160 GSM-7 characters or 70 UCS-2 characters if special characters are used.
Businesses must check the National Do Not Call Registry every 31 days and remove any registered numbers from their marketing lists. Maintain internal do-not-contact lists as well.
Violating TCPA regulations can result in significant fines, legal action, and reputational damage. Ensure strict compliance with all guidelines, including obtaining proper consent and honoring opt-out requests.
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United States SMS Best Practices, Compliance, and Features
United States SMS Market Overview
Market Conditions: The United States has one of the world's most mature SMS markets, dominated by major carriers including AT&T, Verizon, and T-Mobile. While OTT messaging apps like WhatsApp and Facebook Messenger are popular, SMS remains a critical communication channel with nearly universal reach. The market shows a relatively even split between Android (around 52%) and iOS (around 48%) users, with both platforms fully supporting standard SMS features.
Key SMS Features and Capabilities in United States
The United States offers comprehensive SMS capabilities including two-way messaging, concatenation, and MMS support, with strong carrier infrastructure and standardized delivery protocols.
Two-way SMS Support
The United States fully supports two-way SMS messaging across all major carriers. There are no specific restrictions beyond standard compliance requirements and proper registration for A2P (Application-to-Person) messaging through the 10DLC registration process.
Concatenated Messages (Segmented SMS)
Support: Yes, concatenation is fully supported across all major U.S. carriers.
Message length rules: Messages can contain up to 1600 characters before splitting occurs. Single SMS messages are limited to 160 GSM-7 characters or 70 UCS-2 characters.
Encoding considerations: GSM-7 encoding is used for standard ASCII characters, while UCS-2 encoding is automatically applied for messages containing special characters or Unicode, reducing the per-segment character limit from 160 to 70.
MMS Support
MMS is fully supported across all major U.S. carriers, allowing for rich media content including images, short videos, and audio clips. Best practices include keeping media files under 1MB and using common formats (JPEG, GIF, PNG for images; MP4 for video) to ensure broad compatibility.
Recipient Phone Number Compatibility
Number Portability
Number portability is available and widely implemented across all U.S. carriers. This allows users to keep their phone numbers when switching providers. While this doesn't directly affect SMS delivery, carriers maintain a central database to ensure proper message routing.
Sending SMS to Landlines
SMS to landline is possible but varies by carrier and landline provider. When attempted, some carriers will convert SMS messages to text-to-speech voice calls for landline recipients, while others may simply fail to deliver. It's recommended to verify number types before sending and filter out landline numbers from SMS campaigns.
Compliance and Regulatory Guidelines for SMS in United States
SMS marketing in the United States is primarily regulated by the Telephone Consumer Protection Act (TCPA), the CAN-SPAM Act, and Federal Communications Commission (FCC) guidelines. The CTIA (Cellular Telecommunications Industry Association) provides additional industry standards that should be followed. Companies must also comply with state-specific regulations and the A2P 10DLC registration requirements.
Consent and Opt-In
Explicit Written Consent Required: The TCPA mandates obtaining explicit written consent before sending marketing messages. This consent must be:
Best Practices for Obtaining Consent:
HELP/STOP and Other Commands
Required Keywords:
Language Requirements:
Do Not Call / Do Not Disturb Registries
The National Do Not Call Registry applies to SMS marketing. Businesses must:
Time Zone Sensitivity
Time Restrictions:
Phone Numbers Options and SMS Sender Types for in United States
Alphanumeric Sender ID
Operator network capability: Not supported in the US market
Registration requirements: N/A
Sender ID preservation: N/A - Alphanumeric sender IDs are not displayed to US recipients
Long Codes (10DLC)
Domestic vs. International:
Sender ID preservation: Yes, original number displayed to recipients
Provisioning time: 1-3 business days after A2P 10DLC registration
Use cases:
Short Codes
Support: Fully supported across all major carriers
Provisioning time: 8-12 weeks for approval and activation
Use cases:
Restricted SMS Content, Industries, and Use Cases
Prohibited Content:
Content Filtering
Carrier Filtering Rules:
Tips to Avoid Blocking:
Best Practices for Sending SMS in United States
Messaging Strategy
Sending Frequency and Timing
Localization
Opt-Out Management
Testing and Monitoring
SMS API integrations for United States
Twilio
Twilio provides a robust SMS API with comprehensive documentation and strong support for US messaging requirements. Integration requires an Account SID and Auth Token from the Twilio Console.
Sinch
Sinch offers a straightforward REST API for SMS messaging with strong delivery rates in the US market. Authentication uses an API Token and Service Plan ID.
MessageBird
MessageBird provides a feature-rich API with strong support for US messaging compliance requirements. Authentication uses an API key.
Plivo
Plivo offers reliable SMS API services with strong US coverage. Authentication requires Auth ID and Auth Token.
API Rate Limits and Throughput
Rate Limits by Provider:
Throughput Management Strategies:
Error Handling and Reporting
Recap and Additional Resources
Key Takeaways:
Next Steps:
Additional Information: