I dont- but Verisign offer farily competative credit card services.
I assume you have looked through the code library?
my initial thoughts on this would be just to do a dns lookup on whatever the user enters. If you wanna do this, look up the checkdnsrr() function. there are also other functions in the Network section of the php manual that might be useful.
As for registering them, i really have no clue. Maybe Network Solutions has an SDK of some kind?
Arta