I know some phones have the option of using external antennas.

While they may not be much longer than the phone's native antenna, it does allow for one to place the antenna somewhere that may get better reception (say, up a tree or something) without requiring the user to place themselves in danger just to get a signal.

With that said, if I actually needed a cell phone that I could somewhat rely upon in remote places....I would probably be looking into a satellite phone, or at the very least, a modern bag phone (which is still allowed to operate at 2 watts). Typical consumer phones tend to fall short when it comes to rural/remote use.