iPhone 3GS will not make or receive calls.

Over the past week my iPhone (which has worked perfectly for 6 months) had stopped making or receiving calls. My phone will work one minute then 24 hours later, i get 15 voicemails and text messages at 1 time from people that i have been trying to call me. Its as if i have no reception,then it will kick back in all of a sudden. The same goes when i try to make calls. I try to dial and it either freezes or just says 'cant connect' and returns to home screen. Its getting worse as the days go on. Ive restored network setting, updated it on iTunes but it sometimes works, sometimes doesnt.