Unless this has changed in recent APIs, no it doesn't - the web browser does, but otherwise if you open the url "tel:somenumber" it will just start dialing.
I never tried, but assume if you tried to submit an app that wasn't, say, an address book, it would get rejected if their wasn't a prompt first. Certainly if I'd published an app that did that I would have had a prompt.
"Don't try to outweird me, three-eyes. I get stranger things than you free with my breakfast cereal." - Zaphod Beeblebrox in "Hithiker's Guide to the Galaxy"