Samsung C5010 problem?

I have a Samsung GT-C5010 which reboots when i try accessing the phone book. I tried different sim cards but with the same result. The sim cards are 128K sim cards with nothing on them so they are not overloaded with data. I tried hard resetting the phone and also updating it but the problem persists. Calling customer care doesn't work either cause no reps or technicians know how to fix it and the local service centre replaced the phone but i still have this problem!!!