The T-Mobile Samsung Galaxy S II has Android 4.1 Jelly Bean rolling out right now, and I'm walking through the changes from Ice Cream Sandwich.  If you were thinking about the Galaxy S III or even the Galaxy S 4, you have some time to spare, as the Jelly Bean update for the Galaxy S II brings many of the software enhancements (Blocking Mode, Home Screen Mode, and other customizations like text message bubbles) to the Galaxy S II.  While the nature UI elements are missing from the Galaxy S II, Project Butter is on board, along with the updated notification area that you'd expect.

The Android 4.1.2 update is available exclusively through Kies (no OTA rollout due to the size), and can be downloaded for both the Galaxy S II on T-Mobile and Epic 4G Touch on Sprint.