Saki must be living in the luckiest part of the village, having better cell phone signal strength than anyone else. After all, the early chapters made it a point Himeko and Hayato's home had such abysmal reception that the dude never even thought about getting a cell phone. We can assume their school back in the village was no better off since a school kid would be spending many hours every day over there, again justifying a cell phone.
I doubt the situation would be getting any better since 4G and 5G are even more troublesome than 3G for the signal penetration, yet with the declining Japanese population, it wouldn't be financially viable to invest heavily in the networks out in the countryside.