W880 Signal Problem

I have a w880 and i have unlocked it. I was gettin an error "Configueratuion error. Please contact your network operator or service centre" So i flashed it with the custpack and now all is workin and is still unlocked. But my phone will not recived calls ? and acts like it has got no signal even tought the signal bar is near enought full ?

Disable 3G: Menu > Settings > Connectivity > Mobile Networks > GSM and 3G > Only GSM

I also am having same problem but when i select gsm it says no network coverage but with 3g/gsm selection it works sometime & than no network signal though it shows full bars??? Any idea??? Thnks