Pikey... I've heard a lot of people say that email is fine, and that's what I plan to do, particularly since I'm out of the country.
I would contact firms in the area, saying simply that you will be in the city, would be sending a resume and cover letter, and would be available to interview or something like that. But definitely be clear that the firm is coming to your school. I have a feeling that if firms are coming to interview at your school, they may just want to consolidate and review your stuff with everyone else's. BUT the fact that you're already going to be in the city BEFORE OCI may be an ok exception for them.