It's no secret that the Nexus 4 is a hot item. Google Play is selling out of them faster than they can make them. T-Mobile sold out of its initial stock in just a matter of hours, and then it restocked and sold out of that almost as quickly. Well now the phone is back in stock again, but something immediately stands out as being different from the previous listings on T-Mobile.
It seems that T-Mobile is trying to capitalize on the high demand for the device by raising the price substantially. The subsidized price of the device on T-Mobile's website is now listed at $399.99. That's $50 more than Google is charging for the device with no contract. That makes it a tough sell for T-Mobile, with the only saving grace being the fact that Google cannot keep the device in stock at all.
Hopefully, this is a typo on T-Mobile's part that will be fixed, but that seems unlikely. More than likely, T-Mobile realized that buyers are willing to pay a premium to get the device now. Time will tell if the stock keeps moving at the same speed as it did before at this new price. It seems likely that many buyers would be turned off by this new , much higher price tag.
One thing to note is that there is a link that says, "Already a T-Mobile customer? Log in to see your price." Perhaps existing customers will be able to get a lower, more reasonable price for the popular device. Feel free to check in and try for yourself (and good luck), since new contract prices are typically lower than prices for existing customers.