The honest answer is that the provider matters less than the number, and the number matters because of how the BOP prices calls.
Local calls in the federal system run $0.06 per minute. Long-distance calls run $0.21 per minute. That $0.15 per minute difference is where the money goes, and if your inmate is on the phone regularly, it goes fast. Three hundred minutes at long-distance rates costs $63. Three hundred minutes at the local rate costs $18. Same conversations, same phone, same facility. Just a different number on the other end.
InmateAid's phone line gives your inmate a local number to dial no matter where you actually live. The line costs $5 a month, no hidden fees, no contracts, no gotchas. On 300 minutes, the rate difference saves you $45, minus the $5 line fee, and you are walking away $40 ahead every single month.
I spent 66 months in federal prison. Forty dollars a month back in someone's commissary account instead of padding a phone carrier's contract is not a small thing. That is food, hygiene, maybe some new sneakers. It is the best deal going in the federal system right now, and I have not seen anything come close to it.