I was an early adopter… I still have my 4g iPhone. I bought it because I am a long time user of Apple products, as well as palm/windows mobile PDAs. My entire contact list is in AddressBook, and syncing/ connecting my PDAs and phones was always a pain because of proprietary systems and different ways of storing data.
The iPhone was going to solve that problem by syncing flawlessly. I gave away my PDAs, Razr, and sony s710a when I got the iPhone.
Another reason is the mobile Internet. That’s the most revolutionary part, more companies are doing the same because it’s in high demand.
The music, movies, and camera are all awesome as well, and the fact that the phone gets updates and new features every couple of months makes you feel like you’re getting a major return on your investment. They lose value slowly – like all apple products. You can sell a almost-year-old used one for 300–400 dollars.