So prior to the getting the iPhones, how was the Sprint coverage in your area? Was it great like 5 bars and all of a sudden you are getting crappy reception? Have you compared it with any other Sprint device like an Android device in the same area. Perhaps the iPhone maybe defective?
I don't know what you mean by when you see the little "o" indicating 1x data connection so I can't help you. Perhaps a screenshot of your phone will help.