In reply to Rob Parsons:
I spent many years working on radio design (but so no much recently so some of the maths is a little hazy now)... As you say a radio signal decays the further you are from the source, however what determines whether is can be received or not at the far end is signal to noise ratio. Assuming your signal is not somehow hidden by an interfering noise source, you are limited by thermal noise at the receiver (a satellite will have an advantage here that the electronics will be very very cold). Its a line-of-sight link, so you wont get some of the other difficulties associated say with cellular transmission (signals bounding off buildings etc).
Given your signal will be much weaker than your typical phone to base station link, you need less noise, so you typically get rid of (thermal) noise by reducing the signal bandwidth, so if your phone can uplink to a satellite expect the data rate to be very slow - I just checked at the minimum data rate for satellite phones is 2.2kbps, so enough to send encoded speech, but would for example take 26 minutes to upload 1 photo from my Iphone!
This incidentally is why your phone will still carry a 2G chipset going forwards (as well as 4G/5G), as you will always have more range with 2G due to its lower data rate, so if you are in the middle of nowhere its a get-out-jail backup to keep you connected (to the nearest base-station)
Post edited at 10:25