Cannot Send SMS to any AT&T subscribers

Hi Anzen,

That's weird. I myself have AT&T number and I've never had problem to send SMS to that number from my RC number (including my RC sandbox number).

What was the error or you just don't receive the text message?  

Please create a support ticket on the following page with information on specific texts you are sending.

In general, I haven't encountered any issues when sending to AT&T, however, carriers can blacklist numbers when they are receiving what they perceive to be spam or otherwise unwarranted messages on their network.

https://developer.ringcentral.com/support.html