In addition to the 'locked firmware' problem, "Telephone" implies that there is a centralized "telephone network" that can be
surveilled and/or attacked, making for a short revolution.
Wireless device have an interesting property. They can communicate with ANY compatible device within range, as long as it is programmed correctly. Why depend on "the man" (who is typically government regulated, or depends on 'retroactive immunity' in the US), if you don't have to.
Just be more decentralized in your thinking. 10 years ago there was a great gadget called a 'Cybiko', which ran on unlicensed
900 Mhz frequencies, but you could program on your own. The device went through several hardware generations, but doesn't exist any more. It even had an interesting 'walking talkie' application, which converted your voice to a digital signal and sent it to other Cybikos within RF range.
No cell network required.