If they have a way of processing credit cards for on the phone sales they can use
Mal's e-commerce, mal's ecommerce. This site captures the information, sends you an email so you can log in there and retrieve the info and process it yourself. I have a client who has used this system for over 7 years now without a hitch. Since she takes phone orders, she already has the ability to process credit cards.
and...IT IS FREE!
Good luck to you!