Prison and mental health facilities don't let you have a cell phone, period.

Longtime friend called me from one of these places yesterday. I answered only out of common courtesy, fully expecting a robocall.

While I agree with you, some proprietary closed communications channel controlled by a corporation that mines data for advertisers is worse.

I think ideally people should use something like xmpp or email.

Yes I'm sure they can quickly log on to discord from jail.