The important thing to remember is that Sprint have no clue. ... About anything, as far as I can tell.
My first experience with Sprint was of them being the default carrier at a hotel I stayed at in Florida. Well, since hotel phone charges are enormous, I used Sprint directly and was able to just enter my credit card number and have them bill it for a call.
A week or so later, in another state, I tried to use Sprint again, but the automated system didn't offer the chance to put credit card number in as well as calling card numbers. I phoned customer support, and they (at all levels, supervisors, etc) were adamant that this had never been possible under any circumstances.
Of course, my charge from Sprint did appear on my credit card, despite Sprint's insistance that they had never offered such a service at all.