You cannot use them while you travel. Cell networks are also limited in the mobility area. While it is true you can travel, there are many places which have no cell coverage. For example, if you want communication on a ship out in the ocean, you won't accomplish this with cell or land lines. Satellite networks can also provide a greater bandwidth.
Satellite networks show the greatest promise for the future.
With increasing bandwidth and mobility demands on the horizon, satellites are the logical option. The main inhibitor now is the cost. Launching entire systems of satellites into space is an expensive endeavor, with costs in the billions of dollars. But new technology has always cost a lot up front. Just look at the cell phone service.