T-Mobile is running a special $24 discount promotion on the Google Nexus 5. This essentially takes the price of the Nexus 5 down to $372 with service from T-Mobile, even though said service doesn't require a contract.
For comparison, the same 16 GB configuration of the Nexus 5 retails for $349 on the Google Play store. However, going with T-Mobile will allow you to finance the phone and pay smaller installments over time rather than shelling out $349 up front, though in the end you do pay a little bit more for going with T-Mobile for the hardware even after the discount.
To qualify for the discount, T-Mobile advertised in a Twitter message that users will have to enter the NEXUS5PROMO code at checkout. The deal is said to be valid for web orders only so you can't walk into a retail store for that pricing.