I’ve helped several families set up Google voice numbers in the region of their loved one’s prison just to save money.
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.
My boss's friend operates https://phonedonkey.com, which provides a VOIP relay service such as what you set up.