Hmmm, I don't think I've ever called a guy who's given me his card. I take it as being very formal and that he is not really interested in dating, but more in a business relationship. It also would kind of depend on context...I've had guys ask for my number, then say, "well, how about I give you my number and you can call whenever you want." If he happened to pull out a card because it had his number on there but it was qualified ahead of time, then maybe.
Generally speaking, unless I'm REALLY interested in something, I tend to lose cards in my purse, so it's generally a matter of forgetting. By the time I remember or find the card, I'm not interested or don't want to deal with the awkwardness of trying to explain why I have his card and where I met him.
IDK...it sounds complicated when I type it out, LOL.