AT&T offered a statement on Twitter, suggesting users restart their device. If that doesn't work, uh, do it again. "If you've experienced an issue when making wireless calls, please restart your device, this might be required multiple times - that should resolve the issue," the tweet reads.
It's definitely worth trying. The fix is working for many, but others are anecdotally reporting that multiple attempts of the suggested fix haven't improved their lack of service. We'll add any other solutions that may pop up, but remember to be nice to your customer support people. They didn't start the fire. It was always burning since they got into work.