From a press release issued by T-Mobile:
Beginning on June 28, 2008, the ETF for customers who choose a one-year or two-year service agreement with T-Mobile will decline during the course their contract. The ETF decreases from $200 to $100 if customers terminate service with 91 to 180 days remaining on their agreement; and decreases again to $50 with fewer than 91 days remaining. If customers terminate in the last 30 days of their term, the ETF is $50 or their standard monthly charge, whichever is less.
Here's a quick pic:
Not terribly appetizing, though I guess the point is more about staving off regulatory legislation than pleasing customers. Hated Sprint-Nextel is now the only remaining ETF holdout; understandable, given that fleeing customers are its only growing source of revenue.