My iphone 4 cannot make or receive calls, when I call, the number gets dialled, but does not connect and neither can I end the call.

My iphone4 cannot make or receive calls. When I call a number, it dials but does not connect. There is no response when we hear it. And then when we decide to end the call. The phone cannot end the call too. It just shows 'call ending' and won't show the home screen. Then I have to shut it down, to show the home screen. I tried shutting down the phone twice. I also removed the SIM CARD and inserted it twice. But still it won't work. This happened on one more occasion a month ago. That time , when I took out the SIM and inserted it again, it started. But this time it wont start. Please suggest what to do. The phone is out of warranty and is of 8 GB. It is exactly 13 months old. Purchaed from United States, using in Inida.