Got this message last night while in rural Georgia and don't know what it means or how to get rid of it.
It sounds like the phone is in GSM mode. I would check your mobile network settings.
I had this happen to me once and it just happened again. I have an HTC Incredible II and I live in New York City (don't know if that has anything to do with it). Here is how I fixed it:
Power off phone
Open phone, remove battery and remove SIM card
Replace battery and power on phone.
When the phone comes back on it said something like, No SIM card, this phone will now switch to CDMA mode.
Open phone and replace SIM card.
Power on phone - should be fixed. When I power on it says SIM card detected, this phone will now switch to Global mode. The Vodafone NL is gone and everything seems to be working as usual.
Short version:
1. Power down
2. Remove SIM card
3. Power up
4. Power down
5. Replace SIM card
6. Power up
Hope that helps.
