Here is my experience:
1. Can you pre-order an unlocked device? No
2. Can you pre-order an AT&T device full retail price? No
3. Can you pre-order the T-Mo device for full retail without T-Mo service? No
4. Will a device purchased at full retail in an Apple Store come unlocked? No
5. Will Apple sell a carrier unlocked model on launch day? No, that will come eventually, but not for a couple months
6. Can you unlock a T-Mo device purchased at full retail at an Apple Store without T-Mo service? No
7. Can you unlock a AT&T device purchased at full retail at an Apple Store without AT&T service? Yes!
Since I'm on Cricket, I can use a locked AT&T device, so ideally I would have been able to pre-order one last night...but alas the US carriers are a disgusting disease infecting the mobile industry, so that's not possible. Shockingly, with the 5S last year, I was able to unlock a device without AT&T service - all I did was call and say I bought it full retail and I needed it unlocked. That's my plan this year too.
(In my experience T-Mobile is really annoying about unlocking devices when you don't have service with them, even if you bought it full retail.)