A lot. Most of the upper midwest lacks cellular coverage. You need to drive to the top of a hill to even hit a gsm signal at one bar. The old analog signals were better but they're gone now.
My grand parents do not get celluar where they live in very remote Montana. Apparently ether Verizon/AT&T (i can't remember which) has been promising them Celluar/Cable service for over 5 years now, and has never come through with it.
Honestly i think the only reason they even pay for AOL is because they use it to keep in touch with relatives via email.
And it would, except that Charter communications owns rights to the cellular spectrum there. So once such a system were in place Charter would no doubt come in and take it away from you and then operate it at a profit if they could.