LG/LG P500
Phone malfunctioning

I bought LG P500 (Android Phone) in June. After Dec my phone started giving problems. It started hanging, response time was also very high (there was time lag). While typing messages, the alphabets were displayed after 2-3 seconds, after selecting some option, the window opened after 4-5 seconds. I went to service centre and my phone was formatted. It worked nicely for 15-20 days. Again the problem started. Recently phone developed network problem. Whenever there is an incoming call, the network goes off. From the last 3 months, I have been going to the LG Service centre every 15 days, Every time my phone is formatted. All the problems still persist. Last month the motherboard was also replaced, but that did not help either. I am fed up from the phone. Please assist me at the earliest.