It is a lot more economical than people think. In the US, all you need is a Globalstar system that can be found for around $20.00 per week with air time running about $1/minute. Some companies will even do pre-paid minutes that will allow you to lower the rate. Here is one I found with a quick search.

http://www.satellitephonestore.com/satellite-phone-rental.php?OVRAW=satellite%20phone%20rental&OV KEY=satellite%20phone%20rental&OVMTC=standard& amp;OVADID=5519666511&OVKWID=27642500011