I've been researching satellite phones for a while and just purchased a Globalstar GSP-1700. Globalstar's second gen satellite network is now fully operational and working quite well now. They had some service problems during the launch of the new system due to the gen 1 satellites failing. That is not an issue anymore.
As said above, the Spot global phone is a rebranded GSP-1700 and uses the Globalstar network at the same rates. Go with whatever one is less expensive. I picked up my GSP-1700 for $389. The double minutes promotion is still going on so I opted for the Orbit 40. I figure $40/ month is cheap insurance for my life.
Here's a couple of tips...First, you must have a clear line of sight to the sky. The phone reception is also sensitive to having the antenna fully extended and pointed up to get a signal and while talking. I made a call from inside my house at a window and it was just as clear as my cell phone. Globalstar offers standard US based 10 digit numbers and calling is pretty straight forward...dial the area code and number then press send. (This was very important to me) You can also receive 35 character text messages but you cannot send them.
Of the three service providers, Globalstar has the best call quality as it uses CDMA technology, just like Verizon Wireless' digital cellular network. It also doesn't suffer from delays in the conversation. Iridium has the best coverage with the only true global network as the satellites are in a polar orbit. Inmarsat has a few stationary orbit satellites over the equator but doesn't reach past the northernmost and southernmost parts of the globe. Iridium and Inmarsat receive the signal from the phone and relays the call to one or more satellites until it can reach a ground station where the call is routed through normal networks. The satellite 'hopping' is the reason for the delays in the conversation. Globalstar calls transmit to the satellite and then directly back to a ground station as their network has many more ground stations across the globe. No hopping means a faster round trip transmission and thus no delay.
At current prices and service levels, satellite phones are now a very viable communication tool to supplement traditional cell service and provide a life line in those life and death situations or just to place an occasional call while out in the middle of nowhere.