The Samsung Galaxy S II for T-Mobile (SGH-T989) was released in April 2011, with Android 2.3 Gingerbread. Last June the device was updated to Android 4.0 Ice Cream Sandwich and now its getting set to receive a new update in the form of Android 4.1.2.The Android 4.1 Jelly Bean update will include the Samsung's Nature UX Touchwiz interface which is currently available to Samsung Galaxy S III and Samsung Galaxy Note II users.
The update will also include the other improvements you would expect from Jelly Bean, like the performance improvements of Project Butter, the Google Now digital assistant which shows card based information on all your interests and the actionable notifications which allows you to respond to a missed call, or an email, directly from the notification shade itself.
Users will also get features like Samsung's Pop-up Play which is a multi-tasking enhancement which allows you to move a video that you are watching over the screen while viewing a different app. Smart Stay which keeps your display switched on while you are reading content by monitoring your eyes using the front facing camera. You will also get improvements to the device camera, an updated lock-screen with customization options, new widgets from the Galaxy S III and two home screen modes.
As it is common with Android updates it maybe awhile before this one reaches all handsets, so give it a day or two before you look out for the (OTA) over-the-air update notification Once you do receive the notification you can initiate downloading and installing the update. You can also manually check for the update under Settings or by connecting your smartphone to Samsung Kies.
Make sure you are connected to Wi-Fi to avoid data charges and ensure your battery is fully charged before initiating the update.
source - SamMobile