SMS delivery failure to Twilio virtual numbers from eu-west-2 — "Phone is currently unreachable/unavailable"

Question

Hello,

We are experiencing SMS delivery failures from AWS End User Messaging in the eu-west-2 (London) region to Twilio virtual numbers in the UK. This was working correctly until approximately April 30, 2026, and stopped without any changes on our side.

Details:

Region: eu-west-2 (London)
Originator type: Registered UK long code
Destination: Twilio UK virtual numbers
Error: "Phone is currently unreachable/unavailable"
SMS Type: Transactional
Started failing: ~April 30, 2026
Testing performed:

Sent SMS from our AWS long code to a non-Twilio UK number → delivered successfully
Sent SMS from Twilio to the same Twilio destination number → delivered successfully
Checked Twilio inbound message logs → no incoming messages appear from AWS, confirming the message never reaches Twilio's network
No configuration changes were made on our side since it last worked
Conclusion:

The issue is specific to the routing path between AWS's intermediate carrier and Twilio's UK number range. Messages to real UK numbers work fine, and Twilio receives SMS from other sources without issues.

Could you please investigate the routing for SMS from eu-west-2 to Twilio UK virtual numbers and advise on a resolution?

Thank you.

re:Post Agent · Answer

I understand you're experiencing SMS delivery failures with the error "Phone is currently unreachable/unavailable" when sending to Twilio virtual numbers from eu-west-2. This is indeed one of the recognized failure reasons in Amazon SNS SMS delivery monitoring.

Based on the information available, "Phone is currently unreachable/unavailable" typically indicates a temporary issue where the destination phone number cannot be reached at the time of delivery attempt. This can occur due to various network-level issues between carriers.

To help diagnose this issue, I recommend:

1. **Enable CloudWatch Logging**: If not already enabled, turn on SMS delivery logging in the SNS console to capture detailed delivery logs, including the providerResponse attribute which provides specific failure reasons.

2. **Verify Your Origination Identity**: Ensure your registered UK long code is still active and properly configured in your AWS End User Messaging account for the eu-west-2 region.

3. **Check Account Status**: Verify that your SMS account is in production mode and has the necessary permissions to send to UK numbers.

Since you've confirmed that messages to regular UK numbers work fine and Twilio receives messages from other sources, this does suggest a carrier routing issue. However, this type of carrier-level routing investigation would require direct engagement with AWS Support, as they have access to detailed delivery logs and can work with carrier partners to investigate specific routing paths.

I recommend opening a support case with AWS Support and providing them with specific message IDs, timestamps, and the destination numbers experiencing issues so they can investigate the carrier routing between AWS's SMS infrastructure and Twilio's network.  
**Sources**  
[Amazon SNS SMS delivery monitoring with Amazon CloudWatch metrics and logs - Amazon Simple Notification Service](https://docs.aws.amazon.com/sns/latest/dg/sms_stats_cloudwatch.html)  
[Use AWS End User Messaging to send SMS messages  | AWS re:Post](https://repost.aws/knowledge-center/end-user-messaging-send-sms-messages-uk-number)

SMS delivery failure to Twilio virtual numbers from eu-west-2 — "Phone is currently unreachable/unavailable"

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