Having the same issue with Note 3. I just called Tmobile...Here's a "Quick Fix" for internet connection & non Wifi cellular connection simultaneously.
This is NOT a solution, but it helps for now if you have cell service where you use wifi.
(If you have decent cell service where you have wifi this will help) This will take calling OFF of Wifi to receive calls non Wifi &
will also connect phone to Wifi Internet simultaneously by splitting connection.
Call Tmobile with feedback on anymore issues, as they are now aware & working to fix this problem.
STEPS ------
1) Menu
2) Settings
3) More Networks
4) Wi-Fi Calling
5) Connection Preferences
6) Cellular Network Preferred
After changing settings, give it a few mins, then try calling phone from another
phone, cell service will be on cellular signal.