Most of the jail and prison systems I know have technical checks in place for Google voice and other VOIP systems to avoid you getting around their charges. They will ban the numbers and then often ban you from the phone system and sometimes put you in the Hole for games like that.

I used to use them to try to call the UK instead of paying multiple dollars a minute when my mother was dying of cancer. But it's a game of cat-and-mouse. And if you're in a place that makes you wait 4-8 weeks to get a number added to your call list, then you can't afford your number to get banned.

Every day I help multiple guys inside do "3-way" calls from prison to numbers that aren't approved onto their lists yet. It's a dangerous game, though, as the calls are often detected and blocked.

FWIW, my interactions have been with the federal system over 10+ years. I never heard of any blocking of google voice numbers there. It appears to be common knowledge among the inmates as a way to avoid the long distance charges.

That's wild. Google Voice has been my primary phone number since before it was called Google Voice; at this point no one except me even knows my current "real" number. I'd hate to think that someone might get in trouble just for trying to call me from prison.

I worked for a company which offered a bridge between CorrLinks (federal prison email system) and SMS. The inmate would get their own phone number they could receive messages from, and make outgoing texts as well.

My boss's friend operates https://phonedonkey.com, which provides a VOIP relay service such as what you set up.