In the US it wasn't an issue. What was the trouble? Keep in mind I was sending it to one or two people. I have no doubt it doesn't work on a mass scale.
AT&Ts gateway worked for me around 2019. I was sending it from a domain that was set up with all the anti-spam things you have to set up to be a good sender (whatever rules so GMail etc don't dump all your messages right to spam, they are recorded but I don't recall them). It's possible that GMail was blacklisted because a lot of spammers had a ton of Gmail accounts.
Edit: Super important. You can turn that feature off per phone number. You (or your recipients) may have told att not to send them
In the US it wasn't an issue. What was the trouble? Keep in mind I was sending it to one or two people. I have no doubt it doesn't work on a mass scale.