There are a few devices that would allow connection to two (or more) different cell companies at once. Expect sticker shock.
In theory, you could connect to all of the 'big four'. In practise, you, as a user, have no control over the 'back haul' load on the towers.
My brother has a cottage that is 1000 feet from a cell phone tower, which serves a Provincial Park. During the week, it is fast--up to 50 mps down load. On the week end, when every one and his dog is connecting, speed is low low low and ping times may be over 1000.
Maximum range is 25 miles--anything over that and even if the signal is strong, the connection 'times out'.