I might be wrong but I think Zombaio is a gateway, which means you need to get your user/Pass system, billing pages, etc set up, then Zombaio will process the charges... While CC Bill provides everything....
I know CC Bill is SOLID!
I met the guys at Zombaio at Internext and they seams to be very good people, and I know they have been around for a while now...
Hope this will help
