I have a similar problem because I am located in an area with very poor coverage. When I force a search for providers I find that there are 3 in range, two being very weak and the third much stronger. As I have a TMobile sim card, with automatic selection it tried to connect to that tower but that is one of the weaker ones and was constantly connecting and dropping. If I force it to connect (manual setting) to the stronger signal the phone works far more reliably.