Can't receive calls in GT-I5700

Hi,

I bought GT-I5700 and initial 6 months were fine. No problem. But recently, i am not able to receive calls and it is saying as "The mobile customer is not available" though i could see a full signal strength in my phone. But when i make an outgoing call, then i could receive incoming calls. But suddenly i couldn't receive incoming calls. This i notice after someone tells me that i couldn't call you. My phone was still in warranty and give it to service. After service too, the situation didn't improve. The service personnel just wiped out all data and installed android 2.1. I thinking of giving the phone to service again. But is there any other known solutions i can try? I am still skeptical if i give to service also, the problem could be solved. Pls. help.

Kanpai..
Samy..