T-Mobile's Samsung Galaxy S II receives Android 4.1.2
Obviously, the phone will be the recipient of Project Butter, allowing for silky smooth, lag-free movement on the screen. The actionable notifications allow you to respond to a missed call, or an email, directly from the notification shade itself. And of course, there is Google Now, churning out cards with information you need when you need it.
Pop-up Play which helps you multitask by giving you the ability to move a video that you're viewing, all over the screen while certain apps play underneath it. Smart Stay uses the front-facing camera to monitor your eyes to see if they are still directed at the screen. If they are, your phone stays on. If not, your handset gets to go to sleep. Other changes include improvements to the camera, a new lock screen with customization options, new widgets from the Samsung Galaxy S III and two home screen modes.
As usual with these updates, they tend to roll out in phases, so if it doesn't reach your Samsung Galaxy S II today, don't put a call in to T-Mobile CEO John Legere all ready to go off on the T-Mobile executive. The update will come to you via the OTA process, or you can try to coax it out by connecting your phone to to your PC and using Samsung Kies. In both cases, you should probably have a stong Wi-Fi signal and have your battery charged up to at least 50%.
source: SamMobile via AndroidAuthority