Nexus 4's are a hot commodity at the moment, and it seems T-Mobile is feeling the heat. The carrier, who is the only operator partner for the Nexus 4 in the US, has sold out of handsets online, though your luck at brick and mortar stores might be better. This happened mere hours after Google added a link to T-Mobile's website on the Nexus 4 Play Store listing, which is likely being bombarded with more F5's than Reddit in the late afternoon.
It's unknown just how much stock retail locations received, or how many phones T-Mobile as a whole got. Given just how quickly Google itself fell to demand (read: instantly), a tempting link from the Play Store listing probably quickly convinced some impatient buyers that a 2-year contract isn't that bad. We'll let you know if the situation changes.
Thanks, Sam!