Currently Being ModeratedJun 22, 2013 9:42 AM (in response to davidt-)
Settings > General > Reset > Reset Network Settings.
Remove and reinstall SIM
Basic troubleshooting from the User's Guide is reset, restart, restore (first from backup then as new).
Contact the carrier to rule out network/account issues.
If all of the above has been tried, then take it to Apple for evaluation and possible replacement.
Currently Being ModeratedJul 2, 2013 11:34 AM (in response to diesel vdub)
Thanks for the comments. I already did a fresh restore (not from backup) but haven't tried the SIM. I will do so when I find my tool.
How much do Apple charge for a replacement?