Despite Dell's previous statement that the Streak would "not be certified for T-Mobile operation," I've recently heard from a reliable tipster with a proven track record that the upcoming unlocked units will support the 3G networks of both AT&T (850/1900MHz) and T-Mobile (1700/2100MHz).
Currently, the AT&T-locked Streak can be unlocked for use on T-Mobile via an unlock code or Rebel Sim, but because the device lacks the 1700MHz UMTS band, it can only be used for voice and EDGE data on T-Mobile. The only Streaks that can properly access T-Mo's 3G network are the elusive AWS variants, and those are so rare that they may as well not even exist.
The new unlocked Streak shipping with Froyo, however, is said to be busting out of the gate with quadband 3G bands blazing.
It wouldn't make sense for Dell to start selling the Streak unlocked if it would still only work with AT&T 3G, especially since obtaining an unlock code for the current device requires little more than a phone call to AT&T, so although information from a tipster shouldn't be taken as an official announcement, I'm fully expecting to see all four 3G bands listed in the updated specs for the unlocked Streaks. Unfortunately, the estimated ship date for the new carrier-free Streaks has quietly slipped from 12/8 (shown here) to 12/13, so there's no telling when we'll find out for sure.
Thanks, anonymous tipster!