When we moved to Hanksville, we had Consumer Cellular ( ultimately ATT) and it worked OK for phone calls but any kind of data, even pictures via text were not possible. We had to swap to Verizon because it is the only service that is reliable in the entire area including the lake
Now, with the lake and the cell reception, if you even think of loosing sight of Navajo Mountain, you will loose coverage. But every time I go to the lake, or even Ticaboo, (which is pretty often) my phone will start blowing up before I reach the Tony M. turn off, but I won't check my messages until I reach the BBQ shack just because it comes and goes. But again, if you can see Navajo Mountain, you should have coverage with Verizon. Other carriers, I have heard, is questionable. If you have Sprint, T-Mobile, etc. Might as well shut off your phones when you leave Hanksville.