The startup Pigeonly, made by a guy who spent a few years in prison, has exactly that purpose: lower the cost of communications between inmates and their families.

http://www.fastcompany.com/3037785/innovation-agents/how-an-...

https://www.telepigeon.com/

Also the canteen they order, way overpriced. There are numerous inefficiencies in the prison system, and Pigeonly seems like they picked one area, phones, to attack first.