Don't know why you have problems, but we just blame our problems on the local phone company. They have a bit of a monopoly out here, and their service isn't always that great. I can see a tower from my bedroom window, and yet, some days I have no service at that end of the house. We still have dead zones in certain areas, bottom of a hill, bottom of coulees, etc.
You know all those cell phone maps they show on tv, even the one with lots of coverage, well, we're are the blank spot near the Canadian border, in northern MT.