T-mobile is continually working on updating all the top flagships on its network from 2014, and 2013 to the latest version of Android, Android Lollipop, and the two newest to begin work at the carrier are the LG G3 and the LG G2. The support page for Lollipop software updates now includes the current and previous LG flagship devices in carrier testing. With the carrier now testing the software on those two phones, the actual OTA updates for both those devices likely aren't too far off, so consumers on T-Mobile will want to watch their status bars for any incoming notifications about the update.
Prior to the carrier testing, the LG G3 and the LG G2 had to go through the manufacturer development process, which a few other phones are still currently sitting in, including the Sony Xperia Z3 and Xperia Z1s, as well as the LG Optimus L90, the Samsung Galaxy Note Edge and the Samsung Galaxy Note 4. With Verizon Wireless, Sprint, and AT&T all having pushed out the Lollipop OTA to LG G3 users, this makes T-Mobile the last carrier of the four major carriers here in the U.S. with customers waiting to get the upgraded software on their device, which isn't usually the case.
With Android Lollipop 5.1 having recently been announced, and Lollipop 5.0 now in the hands of T-mobile for both of LG's last two flagship smartphones, users will likely wonder if either device will get upgraded to Android 5.1 at some point in the future. It's possible that the LG G3 will end up with it at some point since the phone is only a year old, however, nothing has been mentioned about the stance of either device receiving Android 5.1 Lollipop at this point. Once the update pushes out to users, they can expect the new features like more bold use of colors, and the more prominent animations that are part of Material Design. Lollipop also brings in other functions like Pinnable screens, more security options like guest mode, and new lockscreen notification interactions as well as heads up notifications from regular screens. LG G3 and LG G2 users have a lot to look forward to.