It is significantyly more complicated than that. Not fair to compare sat phones to the SPOT or other EPIRBs because it is much more difficult to obtain and keep a signal for a duplex conversation than it is to send/recieve a small burst of data.
Also, there are two main sat comm systems covering the US. One, Iridium, works pretty well as long as you have good line of sight with the sat constellation. The other, Globalstar, used to be the best but they had some severe technical diificulties which they are still working out by replacing the birds. SPOT is a subsidiary of Globastar but works on a different system which has not been effected at all by the technical problems and I can tel you that I have a 100% success rate using both my gen 1 and 2 SPOT units.
I was an early adopter of the SPOT and was involved in the development/improvement of the SPOT 2 unit and I can tell you that after proper clothing and water it is the most important piece of gear I own.
The SPOT 2 is infinately better, faster more user friendly than the 1 and it does a great job. However, you have to use it properly.
Slot/deep high walled canyons with diminished views of the sky are going to be a problem for any piece of comms gear which means you have to be smart about how you use it. Send messages before you get in too deep, send additional messages when you the opportunity presents itself and send more when you get back out.
Make sure that somebody responsable knows that if they have not heard from you in X period of time that they are to report you as over due to the authorities who will start the search from the point of your last message.
There is no magic bullet guys. The device will help but it all boils down to you, your skills and good old common sense. I have a great deal of practical experiance with wilderness emergencies and I have the means to have any device on the market. The one I have chosen to carry is the SPOT because it works better than anything else I have ever tested.
Wade
www.HardcoreOutdoor.com