sold out. So in effect, you are going from a site which lists the 16GB Google Nexus 4 as being sold out, to another site for the 16GB Google Nexus 4 that shows the phone as being sold out.
Eventually, inventory will be replenished at both the Google Play Store and the T-Mobile website. But what you can do if waiting for an unknown date in the future is not an option, is call the T-Mobile locations in your area to see if any of them have the device in stock. If they do, you will have the choice of getting locked up with the carrier for two-years at the aforementioned $199 after-rebate price,or pay $499 for an unlocked model with no handcuffs. That is $150 more than the $349 you would pay at the Google Play Store for the same exact phone. But you know what they say about a bird in the hand.
The recommendation from the sold out Google Play Store leads to a page for the sold out device at T-Mobile (R)