Drop calls in specific area

I have had iphone for 2+months. Verizon has replaced it twice, but it is still dropping calls. I have to go out of town 2-4 days a week, and when I am out it drops all the calls. The phone does not say "call failed" or anything. It just drops and I am still showing 2-4 bars. I can get in a 10-15 sec. call, and then drop. Verizon has checked the area and the signal should be good. I have had many verizon phones and none dropped calls in this area. Of course by now, I am out of the warranty period, and will have to pay 400-500$ for a phone that works. In the theads I have read, there has been many suggestions-mostly which I (novice) did not understand. Can anyone help me with suggestions which might not cost me $400-500.? Thanks for the time.