You may have seen emails or discussion around a new requirement for sending SMS to US phone numbers. This document provides the concrete steps for Celo Validators to ensure their Attestation Service remains unaffected by the new requirements.

What is it?

A2P 10DLC is a type of SMS traffic that originates from application-to-person (A2P) and uses a 10-digit-long-code (10DLC) phone number. Mobile carriers are requiring message senders to begin registering their brand and campaign to use this message format going forward, especially for SMS sent for marketing purposes. The exact dates are not clear since this is being rolled out in phases.


For Twilio users, it's recommended to use Twilio's Verify API (post 1.3.0). See these instructions for more details.

Test your configuration by logging onto you Attestation Service machine and running:

celocli identity:test-attestation-service --from $CELO_ATTESTATION_SIGNER_ADDRESS --phoneNumber +<TEST_PHONE_NUMBER> --message test --provider twilio

Use both a US and non-US phone number to validate.

Please fill out this 2-minute form once you've completed the steps for all SMS providers.


For Nexmo users, it's also recommended to switch from a 10DLC number to a toll-free number.

See the "Migrating to Toll Free Numbers" section here for more details.

<aside> ⚠️ For Nexmo, you must upgrade the Attestation Service to attestation-service-v1.2.2 to support the correct routing with US toll-free numbers.


To create a toll-free number:

  1. Purchase a toll-free number
  2. Go to Your Numbers
  3. Manage the number and ensure that it is linked with the correct Application
  4. Keep any existing non-toll free +1 phone numbers in your service as this will continue to be used to send international texts