Cell Phone Signal Booster

Cars can have antennas way bigger or in an array that could never fit in a cell phone. It seems there should be some way to enable your cell phone to get a stronger signal in rural areas or dead spots.
This is a great idea and one I have decided to do on my own. I have a cell phone booster in my Bronco, and i can literally get service almost anywhere! It would not be hard for Ford to come up with something like this, especially since they already have Sync, and cell phone integration.