http://www.iridium.com/products/Iridium-Burst.aspx?productCategoryID=9
Yeah, I know; it’s a for-profit company and special receivers are required. But their very new Iridium Burst datacasting service could certainly fit the bill as an internim solution. I can’t find information on how much it really costs, though. It would be instructive to observe how well the service works in practice, and how they actually manage it.