Problem is that Wifi and 4G are on at same time at home, but no data is downloaded.
Solutions that I have found on the web / customer support:
Solution A
1. Navigate to Setttings -> Wireless and network -> Mobile networks
2. Uncheck Use packet data
3. Wait for Wifi to reconnect
4. Re-check Use packet data
5. Wati for 4G to come on and then dis-appear
Solution B
This happens whenever there is an app running that requires 4G and can't communicate over Wifi, most likely the T-Mobile My Account app. Try launching it (to bring it into the foreground), press Home, and then go to the Task Manager app to kill it.
You could also try Llama from the market and try the following - it has worked wonders for my battery as well.
Turn off T mobils contact sync
menu -> settings -> accounts and sync -> uncheck T-Mobil contacts
Ensure mobile data is not active when connected to wifi - here is how
Install Llama from the Android Market
Add an event called WiFi
Add condition: WiFi connected (any network)
Add action: Wifi Sleep Policy (never sleep)
Add action: toggle Mobile Data (off)
Add another event called WiFi Disconnected
Add condition: WiFi disconnected (any network)
Add action: WiFi Sleep Policy (Sleeps when screen turns off)
Add action: Toggle Mobile Data (on)
This will clear up the dual wifi 4g issue + save you some battery 
