I am having a similar issue. As of Sunday [it is now Tuesday] I have not been able to send or receive texts. After calling the Apple Support and AT&T support, resetting my phone's network 5x, powering off/on my phone 15x, had the data plan removed, then restored on my phone 2x, the problem still persists. I even removed my SIM card from one phone and placed it into another. When I did this, I was still unable to send a text message from this different phone. The problem is obviously with my SIM card and not my phone [thank God!], so I will be calling AT&T to receive another.