T-Mobile has just released a statement regarding its availability of the upcoming Samsung Galaxy S4. Although no specific date was given, the carrier has put up a "pre-registration" page where you can enter your email address to receive updates.
T-Mobile is excited to partner with Samsung to bring the Samsung Galaxy S™ 4 to our customers. We look forward to sharing more information soon; meanwhile, please visit our Samsung Galaxy S4 pre-registration page.
Prominently displayed underneath the shadow of the Galaxy S4 on the registration page is T-Mobile's new "4G LTE" logo, which makes it pretty clear that the latest device will indeed have T-Mo's new network on-board.