Not all end users can receive messages from Twilio short codes. Some end users may use wireless carriers that Twilio short codes don’t support, and some of our supported carriers’ wireless plans don’t include short code messaging capabilities by default.

Twilio recommends that you use Message Delivery Information to identify undelivered short code messages, and configure your messaging application to re-attempt these messages using a long code instead. For more information, check out our documentation on sending messages and understanding message statuses.