All the major carriers are employing extra services in areas affected by the tornado in Oklahoma City. Cox Communications reported that thousands are without Internet or phone service. Some carriers are waiving overage charges during the disaster. You can text donations to help out victims.
If you have trouble getting through to Oklahoma City, it is reccomended to send text messages which don't use as much bandwidth as voice or web browsing.
AT&T is coordinating with local authorities and deploying additional resources.