I'm assuming you're an existing customer, right? Call up Customer Relations and have a chat... I'd aim for the 500mb data plan (because it's cheaper) with unlimited data for the first 3 months so you can determine your data use without getting penalized. I have a lot of friends with the iPhone and they don't go over 500mb/month. If you do, just upgrade to the 1gb plan and for your use, $5 more isn't a big deal and you might even get that difference credited too.