Dell still hasn't announced an exact release date for the Streak in the US, but it appears that the Android tablet is already all prettied up and ready to go. It's really just waiting to get the green light so it can charge out of the factory doors.
The US version of the Streak is unlocked (as you know) and ready for use on both T-Mobile and AT&T. Unfortunately, the list of supported UMTS bands (2100/1900/850MHz) on the device's box means you'll get 3G on AT&T but not on T-Mobile.
And speaking of the box, it is clearly very different from the one I have from the UK, with the slate being displayed in a plastic showcase attached to the top of the cardboard accessories box. It's very striking and definitely won't "fool" buyers into thinking the touchscreen extends to the edges of the device.