If you send a message containing a hyperlink or email address from a Twilio number to an AT&T number, AT&T will block that Twilio number across its network with

If you send a message containing a hyperlink or email address from a Twilio number to an AT&T number, AT&T will block that Twilio number across its network without any notification. This happens even if you have an ongoing thread going with the customer. Even if after the block happens the customer pings the bot with "START" or any message, AT&T silently ignores it and continues to block the number. The customer can continue to send messages inbound to the number (and I believe those get received by Twilio but can't quite remember) but any outbound responses are blocked by AT&T from making their way to the customer, even though they're marked delivered by Twilio. This was the case as of Feb 2019. It could've changed since then and I haven't checked recently.