If you haven't bought your T-Mobile branded iPhone yet, the price has just gone up by $50. T-Mobile has increased the price of the iPhone by $50, causing the new down payment to be $150 rather than the $100 it was at launch. T-Mobile is still requiring customers to make 24 monthly payments of $20.
This effectively raises the price to $630, up from $580. Interestingly enough, the new price offered through T-Mobile is still lower than that of an unlocked iPhone 5 directly from Apple, though not by as much as it used to be. Furthermore, T-Mobile is offering a payment plan, something not offered by Apple.