The iPhone 3g would be the first modern "smartphone" from Apple; before that it didn't allow adding more applications, same as the "dumb phones" before it.
It just had a capacitive touchscreen and a better web browser
Even then, the batteries weren't glued in and it was significantly easier to replace
The App Store was there since the first gen. Steve jobs announce already included it and there were dummy apps like pretending to drink a beer from the iPhone.
With the iPhone 3G they changed the SDK in a way that either you released apps for the first two gen or for the newer generations that made the fist two generations almost useless (planned obsolescence you said?)