Hi right now I have a samsung impression (which doesn't have a data plan) which Ive had for 3 or 4 months. My question is, is it possible to upgrade from my impression to an iPhone 4 and how much additional money would it be for the upgrade (separately from the $199.99 cost of the actual iPhone)? Any help would be helpful, id especially appreciate input from at&t employees or people who have done something similar. Thank you