LG G3 owners who are willing to hop on a computer and use LG's support tool will be able to update their T-Mobile LG G3 to Lollipop.
The Lollipop update for the T-Mobile LG G3 is now available through the LG mobile support tool. While the update doesn't appear to be pushing out over-the-air yet, a quick connection to your computer will allow you to update now. The LG tool, which can be found here, will allow you to update to Android 5.0.1 without erasing anything from your device.
You'll want to start by connecting the device to your PC and using the tools on your phone to ensure your drivers up to date. You do this by tapping on the USB icon in the notification tray and using the Menu button in the top right of the next screen to install PC Software. Once the device is connected with the tool running it may show that your software is up to date. If this happens go to options, then flash recovery. This will begin the update, which will bring you to version D85120b. Early reports say that both Wi-Fi calling, and Voice over LTE (VoLTE) are working after the update. If you can't wait for the update to roll out OTA, be sure to give this a shot and let us know how the update goes for you.
Thanks for the tip, Dustin!