I have no experience concerning iPhone development.
I don't think that you will be able to employ Prolog when developing for iPhone. But since Prolog is declarative logic programming you will learn to think differently and this will be a benefit to you as a programmer in general.
Edit
Using Prolog is a completely different from of programming than the usual procedural way. It's similar to how functional programming (which seems to be somehow hip currently) is different, too.
By solving problems in a different way (or by being forced to solve them in differently) you get a better understanding of what programming/solving problems is about. You'll write better Objective C code after learning Prolog or Lisp.
Concerning academic AI: I suggest learning a functional language instead of Prolog, since Prolog is kind of a niche programming language suited for very special problems. The functional languages are a bit more all-round.