Well, T-Mobile hasn't really said anything about the Dream/G1.
Frankly, I'd be surprised if they did start pre-sales tomorrow, since their big "announcement" is supposedly coming on Sept. 23rd. The 23rd also marks the date that 3G rolls out in Washington (T-Mobile's headquarters are in Bellevue). I'm guessing that's when they will outline the actual features and pre-sale info, and then phone will release mid-Oct. as rumored.