One of the downsides to Google's Nexus sales model is that, if you want to get your hands on a Nexus 4, you have to order one. Thankfully, T-Mobile is also going to be carrying the newest flagship phone. If you want to save some money up front in exchange for a 2-year contract, you can pick up the device for $200. It's currently available online here, as well as in select stores.
Oddly, if you want to buy the phone off-contract from T-Mobile, it's going to run you a jaw-dropping $500. The handset is the exact same hardware that's being sold by Google, so there's no real reason to spend the extra $150 unless you really like T-Mo and feel like being generous.