Interesting. You mean that if you purchase a Twilio phone number for the Mexico region, that Mexico region phone number can’t send SMS messages?
The notes on the Twilio MX guidelines page aren’t super clear, but it seems to indicate that SMS is supported for normal phone numbers (‘long code’)… though with some restrictions.
It says that Two-way SMS is supported, but under the long-code (local) restrictions it says:
Only mobile operator AT&T Mexico supports message delivery from a Mexico domestic long code. It could only be used to send Person-To-Person (P2P) messages.
And further above that in the general compliance considerations it says:
You should not use Mexican mobile numbers to send marketing, one-way, or application-to-person (A2P) traffic. URLs and brand names are some of the A2P content likely to be blocked when sending from Mexican numbers.
Under international restrictions it says:
SMS sent with international long codes will have the
senderIDoverwritten with a random local long number or short code to ensure delivery.
So it’s not super clear to me what they were trying to say about ATT Mexico… it seems bizarre that they would be the only one on to support SMS delivery from a Mexico long-code.
Have you tried getting a Mexico number and trying to send a message? If you want to PM me your phone number, I’d be happy to try to send an SMS from one of my test US numbers as it sounds like Twilio should handle that.