This offer is only available through this "secret link". There is a test 🙂 - the process to get to order is not as simple as we would like it to be, but hey, you are saving a $300 dollars (via rebate): Select "Save on the latest devices from T-Mobile" in the next page select "Click Here for Discounts" then "View Products" and last "Handhelds and PDAs"
The $49.99 is only for new activations, does not include activation fee, and only requires a one year commitment, which is pretty good. The better news is that you will be able to upgrade it to Windows Mobile 6 via a sofwtare download soon.
UPDATE: To get the 1 year contract you must playe your order over the phone - please call 1-866-464-8662 and metion promo code: Windows Mobile
2nd UPDATE: No, you can't get this offer at retail