Check on this because I could be wrong, but I think you can add the new line with data fee on the iPhone and then switch lines between the blackberry and iPhone. Then activate a basic phone on the blackberry line and drop the data plan. This way you get to keep your old number (if you want to) on your new iPhone and it should only cost the extra $10/month on the new line (which will now have a basic phone). I'm fairly certain I've seen this done.