there are a few options you have.
One is there is get google sync on your blackberry and have it sync up the BB contacts with a gmail account.
Then on the iPhone use the exchanged and hook that up to that gmail account and it should import all of your contacts. This is how I got all my contacts from my BB to my iPod touch but then again my main email account is a gmail address so it really is a non-issue for me. everything is stored in Google's cloud.