John Clark is right. Although you can't use your BB on an iPhone data plan, simply because the BB data plan is totally different and has different requirements...you can reverse it and use your iPhone with a BB plan. I actually posted this same thing on Howardforums, and the majority of replies supported this.
If you use your iPhone on your BB plan, all the functions will be present except for Virtual Voicemail. That comes exclusively with the Apple data plan.