Are you also seeing the signal bars go dark with an "X" above it indicating no signal? I have been seeing this only when in 3G only area. (No LTE or Spark) Wen't through about 2 hours of troubleshooting for this and based on what I was told, this is a known issue that is supposedly being worked on. Went through all the steps that she was instructed to do to fix the issue. This wasn't the normal "turn your phone on/off, set your data to 3G Only, Update you Profile, Update PRL" kinda crap. This was re-provisioning/activating the phone, resetting the phone though ##727856#. She also re-provisioned my account, removed the phone from my account and added a different one. And a whole lot of other stuff. Bottom line I was getting the same error message plus not sending receiving text/calls and my signal just dropping off the face of the earth connected to a known good tower (with low signal) and via my Airave.. After all that, I I do mean after everything she tired, she said that it was a known issue that they are working on with HTC for a solution. At this time they are not sure if it is a hardware or software issue. But because it is a known issue and nothing else worked with the instructions they were provided, they are sending me a new phone.
You should have a SIM card. Check your box to make sure you don't have a card with a SIM card attached. If not they you need to go to the store and get one.