The confusion is understandable because there are a lot of services competing for your attention, and not all of them are straightforward about what they actually do.
Here is how to think about it. GTL, now rebranded as Viapath, is the phone carrier contracted to your husband's facility. If GTL holds that contract, every call he makes goes through their system regardless of what number he dials. You cannot replace GTL. What you can do is change the number he dials to reach you, and that is where the savings come from.
InmateAid's phone service works by giving you a number that routes your calls through a lower rate tier within the same GTL system. The inmate still uses the facility phones. GTL still carries the call. But the per-call cost drops, sometimes by 50 percent or more, depending on what rate applies to the number he is currently dialing.
InmateAid will not issue a number if it cannot save you money. If the analysis shows no meaningful savings for your specific facility, InmateAid will tell you that upfront and refund the charge. That is a straightforward policy that removes the risk of trying it.
As for a banking or debit card, that is a separate product that some services offer to let inmates access funds for calls or commissary. It is not a phone rate solution on its own and will not change what GTL charges per minute.
The simplest path is to check with InmateAid first. Tell them the facility and the number your husband currently dials. They will tell you whether a better number exists and exactly how much it saves. Start there before spending money on anything else.