WiFi works great! Works well for me in the Seattle area.
Current: Samsung Galaxy S5, 16GB with stock ROM
Former iPhone 4 owner on ATT. Switched the week my contract was up to T-Mobile. w00t!
Former Samsung Galaxy SIII SGH-T999, 16GB and 32GB miniSD card, T-mobile with stock ROM
Tablet(s): Google Nexus 10, 32GB with stock ROM, Google Nexus 7, 8GB with stock ROM