Why can text messages be sent to other people's mobile phones via satellite?

A small part of it is transmitted by satellite, such as the signals of ships in the sea. After all, satellite communication ability is limited, and most of them are transmitted by mobile base stations (signal towers) and connected by optical fibers. When sending a short message, the signal is transmitted to the signal tower in the form of radio waves. After being processed by the signal tower, the signal is transmitted to the signal tower nearest to the destination mobile phone through optical fiber, and then transmitted to the destination mobile phone in the form of radio waves. In the case of satellite transmission, both transmission processes are transmitted by radio waves.