Are you referring to the contract extension? All carriers require you to sign an extension to your contract if you want a subsidized device. The extension is from the day you sign, not two additional years to the end of your current contract.
AT&T jacked up the price for all its personal unlimited data plans.
I can't find a reference on their site about the old or new iPhone, but if you bundle a smartphone with a data plan you pay $30, otherwise they list their PDA Personal plan at $35.
It is too much to think that this price change was only based on the iPhone 3G launch.
It may be market driven and for HSDPA speeds vs EVDO, AT&T is competitive.
Anything can happen until the official rollout on july 11th...