Recently I was driving in an mountainous area near Taos New Mexico and came upon an automobile accident.
A young man had hit a deer with his jeep and was injured.
He had tried to call for help on his cell phone but had no signal. Luckily I had purchased a dual band repeater type cell phone booster and external antenna for my Explorer. It works by amplifying your cell phone's puny output (around a quarter watt) to the full three watts allowed. It works with any phone except Nextel and anyone sitting in your car can have their call amplified, including two phones at once.
He crawled into the passenger seat and I dialed 911 for an ambulance and wrecker. He was amazed that he suddenly had a signal and called his wife to let her know what had happened.
This stretch of road only sees a car about every half hour this time of the evening and although his injuries were relatively minor I was able to help him call for help thanks to the cell phone booster.
If you travel in areas that have fringe cellular coverage a booster is the only way to go. Because it works as a repeater using a small antenna in the cab and another outside, you do not need an adapter connected directly to your phone. Therefore it will work with any cell phone as well as cellular aircard internet.
Many long haul truckers use repeater type cell phone boosters as well as emergency personnel in rural areas.
Cell phone boosters help in the city or country. I alleyways and under bridges in the city they can help give your phone the boost it needs to reach the tower. Out in the country is where they really shine though. You may notice that you do not have dropped calls anymore after hooking up a booster. Many come with AC adapter kits that enable you to use them at your vacation cabin or home. You will want one that is a Dual Band model, capable of both cellular and PCS frequencies. One very good model is the Digital Antenna Dual Band Booster.
Here is more about cell phone boosters. http://www.ehelpfultips.com/how_to_get_better_cell_phone_rec.htm