Earlier quoted context omitted.
> Using a cellphone is voluntarily, too. Indeed. But the difference is that it is legal (and possible) to program a very open (and privacy-conscious) messaging service. On the other hand, it is completely illegal (in the US by FCC ruling) to develop a completely free and open baseband processor and use it. It is also nearly impossible to set up an alternative cellphone network since you need licenses for using the pa…
You can develop a phone using open band (CB radio for example).
Also in CB bands you are not allowed to encrypt the sent data. Thus not an option for people caring about privacy.