If you’re working in a sensitive location and/or you’re unsure about relying on cell coverage for any reason, talk to vendors like…

http://www.telestial.com

http://www.outfittersatellite.com

http://www.satellitephonestore.com

The cost will likely be prohibitive for many of us… unless you’re about to be kidnapped and you need to get a call out. Then the cost will be minimal. :-)
Why? With a satphone, you have the ultimate “high ground.” If the bottom drops out of the government and cellphones become useless, satphones still deliver.

Why might you not want to rent a satphone?
*** Some have ventured a guess that it raises one’s profile with immigration and customs officials (to my knowledge, this is totally undocumented, by the way). They might think of you as “C.I.A.” or, just as bad, a drug runner.
*** Satphones are expensive. Phone rental might be $8-15/day. Airtime will likely run another $1/minute, even with the newest plans (such as those from “Spot”). Incoming calls are free, along with text messages. But it’s usually the outgoing text or call that means the most (e.g., “We landed and we’re fine.”) (Note: there are now other, less expensive solutions for this purpose. See SpotMessenger, for example.)
*** Satphones have to “see sky” to function well. This can be unhandy in winter climates or in sensitive situations.

Remember, “Half a sky” won’t do. (You can’t call from indoors or in a car unless you install an external antenna.) Costs will run somewhere in the $6-12/day, depending on the unit you choose… and throughput charges are extra. Plan on $6/megbyte. For perspective, your 10 mega-pixel camera probably captures a 5-megabyte image. Ouch. Expensive. Use a SpotMessenger-type beacon if it will get you by.