Revolutionary? I don't know. It certainly sold and was popular but for me in 2007 I would have had to take a step back:
In 2007 I had:
Bluetooth with AVRCP and A2DP, would have had to give that up
Cut and paste, would have had to give that up
Outlook synch, don't know if first gen could do this
Music, choice of music players with better features and better equalizer,
Music synch, nope, not as simple as Itunes, however drag and drop is not that hard.
No voice recorder
No Slinging
And before there is allot of: Well I don't use bluetooth, doesn't matter. The fact is it was out there and people were using some of the above.
Appstore, I don't think there was an app store at first, however I had mutiple sources for Apps, like Handango. And no, Handango does not have 140,000 apps, however they existed in 2007 and we had some choice.
Better browser, probally Safari, however what was the network used, Edge?
Not knocking the first gen, but for folks that had the above, going to a first gen was going backward. I do find fault with other manufacturers of phones, why did they have to be so big and thick, iphone first gen form factor was definitely revolutionary, and so was the UI. However for me UI is now a bit cumbersome.