In an web only offer you can get a free Plantronics M25 Bluetooth headset, plus, save $50 with promo code GS4PROMO by visit their sales page here (When ordering Samsung Galaxy S4).
Switch to T-Mobile and get a $50 promo card. For a limited time, get a $50 promo card for in-store purchases when you transfer your number to T-Mobile.
Shop the Holiday Gift Guide and get 25% off their accessories.
For more on the T-Mobile holiday sales visit their sales page here.