Currently Being ModeratedDec 30, 2012 8:28 AM (in response to nrodman)
You'll get the best answers if you give some actual details about the problem. What does "I'm having trouble makind and receiving calls" mean? What happens you attempt to make or receive a call? Are you having trouble connecting? Hearing? Are you having trouble sliding to answer? Are you getting any error messages?
While you're thinking about that, try resetting the phone by pressing and holding the power and Home buttons until the silver apple appears. It may be a generic answer (to your generic question ) but it fixes a lot of things and takes less than three minutes to try.
Best of luck.