Help Problem: Phone reboots while I'm on call

[raommn]

I purchased this phone 2 days ago, and I'm not sure where the problem is. While I am on a call the phone reboots automatically. There is no clear pattern why. I turned off wifi, and turned off many synchronization settings assuming that they may be overloading the processor. But I continue to face the problem.

I have android OS 2.3.6.

Please Help

Thanks
Narasimha