I was traveling overseas and had forgotten to try and get my phone unlocked before leaving. I called Cingular from abroad and they gave me the unlock code over the phone and the unlocking worked immediately. I had no trouble buying a local SIM and using the phone. When I returned to the US, I inserted my cingular SIM but could not get service (the radio would turn on, search for network, and time out).

I went to a Cingular store where they went through troubleshooting and agreed to ship me a warranty replacement.

Anyone else had this trouble or have thoughts on why this might occur?