Today's Performance, page-160

That's were the cost of satellite phones become the issue. If Iridium gave the un-serviced markets a $5/month SMS only plan with a sat-phone included it would bring in a fortune (it might cost an even bigger fortune though).
Use this hypothetical. There are 186 million Nigerians earning on average $800/month. If each were to spend only $5/month on communications services that would be over $11 Billion a year. Of cause not all Nigerians need or want the service, but 186 million customers from across the entire equatorial region (or world) isn't unthinkable. I did make up the $5/month number, but it wouldn't be an unreasonable expense to someone making $800/month.