They already do. After I left prison I was hired to tidy up the transcripts of the calls as the AI they used wasn't great on prison slang. All the calls were flagged by the prosecutor's office for illegal activity, but they were all the opposite when I listened to them. It was sad.

They already are cheap VOIP services too, you can hear the high level of digital compression on all the calls.

There is a high cost probably in maintaining all the handsets inside the facilities.