It may not be in stores yet, but you can still get the Samsung Galaxy S 4 for T-Mobile via their online store.
Released - Monday April 29, 2013
Carrier: T-Mobile (online only) In all stores May 15, 2013
Full Price: $629.99
Down Payment: $149.99 - Monthly payment: +$20 for 24 months
Hot Features: 4G LTE capable, 5" Full HD Super AMOLED screen, 13MP camera, full HD 1080p videp capture and playback, Android 4.2.2 (Jelly Bean), Samsung WatchON with integrated IR Smart Remote, Air View (Hover to preview content & information)