Electronics360: "Video: Verizon educates consumers on SATCOM"

But SATCOM is affected by obstacles. You need a clear view of the sky and a sufficiently dense constellation of satellites such that as one satellite is passing out of view, another one is coming into view and the network can hand off the connection from one to the other.

I'm sure it's better now, but twenty-something years ago, Iridium calls were notoriously unreliable in Afghanistan. You would get a call connected, but in a couple of minutes or so, the satellite would pass out of view and the call would not be successfully handed off to the next satellite that was currently in view. The more mountain ranges around you, the worse it was. It was better than nothing at all but the more clear sky you had, the better your chance of keeping your connection.