But this won't be like the last time when all of those who were on the original iPhone missed out on all the 3G features?
The primary difference between the original iPhone and the iPhone 3G is the original iPhone is not a 3G network compatible phone, and AT&T's 3G network is not available everywhere.
The iPhone 4 will still be "compatible" it just won't be able to run on the 4G network?
Correct. As AT&T starts rolling out their LTE (4G) network in select major markets only at first, AT&T's existing 3G/EDGE/GPRS network will not be going away in those markets. Both will be available and remain available for a long time after AT&T's LTE (4G) network is expanded to all areas where they plan on making it available. There are still plenty of AT&T subscribers with "dumb" phones - phones not in the smart phone category which are not 3G network compatible phones, which is primarily for internet access via AT&T's cellular network only - for faster internet access via AT&T's cellular network with phones in the smart phone category that include internet access.
And by what you are saying, it will be a long time before the 4G network is fully rolled out to the entire nation, correct?
I'm not sure how long AT&T's scheduled LTE rollout will take for all areas where they plan on doing so - probably over a 2-3 year time frame, which should be available where AT&T's existing 3G network is available now at a minimum, and AT&T's 3G network is not available across their entire network coverage area.