It looks like T-Mobile is rolling out the Galaxy SIII Premium Suite. I turned my phone on this morning (5/13/13) and had a software update. I guess the biggest thing people were interested in is the multi-window/multi view option. It has a sidebar tab you pull swipe to open and drag apps to your screen and gives you split screens that you can resize.
Device version now reads: Android version 4.1.2, baseband version T999UVDMD5, build number JZO54K.T999UVDMD5
Device version now reads: Android version 4.1.2, baseband version T999UVDMD5, build number JZO54K.T999UVDMD5