Now that Google Docs is back up and running, it's apparently AT&T's turn to take a stumble. Customers have reported trouble making calls for the last couple of hours, however, the company said the problem can be resolved by restarting your phone (it may take multiple restarts). There's no word yet on the root cause of the problem, if we get more information then we will update this post.
We are aware of an issue affecting some users' ability to make certain wireless calls. These users should restart their devices, which should resolve the issue.