Post by Steve Manley
The way cellular phones work they use zones or small base stations called "cells". As you move from one area or "cell" your call is "handed off" from the old to the new cell. The switch to the new cell is accomplished by the sending of a special signal to the mobile unit. The Mobile Telephone Switching Office or MTSO connects the cellular calls with the Public Switched Telephone Network or (PSTN). The MTSO also controls all the cell sites. All the cell phones are registered with the control channel so the system knows where to find the cellular phone.
Imagine in a perfect world the cells or zones looked like a large honey bee cone that covered the planet. But this is not possible. It is not cost effective for the cellular providers to put up cell towers in rural areas or many third world countries where there would be low usage. So this makes vast areas of the U.S. and other countries where a cellular phone does not have coverage because if you are not close to a cell tower your cell phone will not work. There is also the issue where your friend's cell phone may work in an area or "cell" and yours does not. That is because their phone is most likely using another cellular provider the uses a tower with a difference technology other than the technology compatible with your phone. Also it would be impossible to place towers out in the ocean far from land, again making your celullarl phone worthless when not close to a cell tower.
Satellite Phones do not use "cells" or cell towers. The most popular hand held satellite telephones use Low Earth Orbiting or LEO satellites. When you turn on your satellite phone the signal goes up to any number of satellites in a compatible constellation where it is then registered with the constellation. Globalstar has 48 satellites and Iridium has 66 that orbit the earth. When making a call the satellite signal goes to the satellites this it is directed down to a ground station or gateway where it is directed by the gateway the to the call destination. The call can be directed to a land-line or PSTN as well as a cellular network. The reverse is also true. Any land-line or cellular network can call satellite phones. The Gateway processes and takes care of the switching of the calls rather than the satellite network. This allows you to use your phone even when you are in the middle or no where far from any cell tower. If you call another compatible satellite phone the call is transmitted up to the satellites and then down to the ground station then transmitted back up to the satellites then down to receiving satellite phone. This is the ultimate secure calling because the encryption is handled at the ground station because the call never goes to a land-line or PSTN.
For more information on how this works go to this link http://www.globalcomsatphone.com/about.html