At first I was skeptical that other satellite phone companies would use geosynchronous satellites but I looked up https://www.inmarsat.com/en/about/technology/s

At first I was skeptical that other satellite phone companies would use geosynchronous satellites but I looked up https://www.inmarsat.com/en/about/technology/satellites.html https://www.inmarsat.com/en/about/technology/satellites.html and sure enough they do