Apple has sold iPhones that were unlocked in the same sense for some time now, and AFAIK, the existence of these phones has not been one of the mechanisms that enabled hackers to unlock the iPhone.
You already can buy an unlocked iPhone... for $599, its full price.
If you want to buy a $99-299 iPhone, its cheaper because the cell phone carrier is subsidizing the cost, and they lock the iPhone so you continue to use their services.
am I just dreaming or do you think this could really happen?
If AT&T is subsidizing the next gen iPhone, it will be carrier locked. The difference with the iPad is that you are buying it outright, away from the carrier.
Yes, but AT&T does not subsidize contract-free iPhones; yet they are still carrier-locked.
The iPad uses a new Micro Sim, try finding another carrier that uses those (TMobile in the US does not), I bet they switch to those in the next iPhone as well to make it even harder to use on another carrier.