phone with antenna

One of the problems I have with my cellular phone was the strength of signal in varying places. When I am in a building, the signal is really strong but when I go mobile, the signal weakens. I never figured out what was wrong. At first, I would bring the unit to a service center but even the repairmen can't detect what was wrong with the phone. It was only until a friend mentioned about a cell phone repeater that I might need to install in my car to make sure that my phone's signal is always detected even when I'm on the go. Will give this a shot.