No. If you have the iPhone 3G, your data plan will be $30/month minimum. Whether you live in a 3G area or not. AT&T is upgrading their network everyday and expects 70 more metropolitan areas on 3G by the end of 2008.
No. As far as we know, our original contracts would stay the same if we don't upgrade to the 3G version. Typically, AT&T doesn't increase your contract until you upgrade or change your contract. Even if your plan is no longer offered, you are able to stay at that same level as long as you keep your account current.