The T-Mobile Galaxy S II has been rooted, thanks to Samsung releasing the kernel source. Like most Samsung Android phones (and tablets) there's no trickery involved, you simply flash the new recovery with ODIN and you're able to flash unsigned update packages, like the one that contains the files needed for root. The process is pretty easy, thanks to no locked bootloaders or rolling back to engineering builds, and we like easy.
You'll need working Windows drivers, and ODIN 1.8.4 or higher, but all the root packages and files are available at the source link, as well as easy instructions to get you on your way. Goodbye T-Mobile Mall, and hello Root Explorer! We're sure plenty of hacks will soon follow -- T-Mobile and Android hacking go hand-in-hand.
Source: Rootzwiki. Thanks, Mario!