sysmaster can do it if you have their gateway and billing
it is called account recharge.
The customer must originally sign up. If he needs to recharge, he can do it through the IVR withphone prompts or do it via the web.
The Voicemster is now version 2.0
You can do the solution with the gateway for about $25,000 to $35000 depending on your requirements.
I would e-mail the email@example.com
or call them. check out the website for the number.
This company is at every trade show. They have a following. Of course there is negetive BS, but we all know people talk crap about alot of things.