Verizon apparently had an "unscheduled outage" on their 4G LTE network nationwide, this morning at about 2AM CST. As of around 6AM there were still many cities that had not come back up, although various reports came in that rebooting your phone could potentially fix the issue. As of this time most reports indicate everything is okay now. If you are still experiencing this issue, sound off in the forums, and try rebooting your phone. If that doesn't help you should probably contact VZW.