Do you know alot of people with iPhones?
Every person I know here has the 500mb data plan. Why? because $5 a month adds up when your not close to 500mb anyway. And its actually more then $5 if you bundle it. It would cost me an extra $10 to go back to my 6gb plan. If they still offered that. So now it would be $10 more for 1gb vs 500mb.
I know quite a few people with iPhones... and not one has the $25 plan.