Chris asks: Can these devices be purchased and given as gifts?
No. You will need to walk out of the AT&T or Apple store with the device activated.
Greekjgg asks: What if I want to buy one for work which already uses AT&T for company account? I can't activate in store, obviously, so will it be possible to to buy without a contract?
We don't have details yet but iPhones for business use will likely be provisioned through your company's IT department.
Tons of people ask: If I purchase an original iPhone from a friend will I be able to get the old data plan pricing? Or will I need to sign up at the new, more expensive rate?
Yes. You can get the old data plan price if someone gives you a device and you establish service for yourself.
Previously: Reserve your iPhone 3G now!