The Galaxy S II for T-Mobile was the last variant of the Galaxy S II in America to launch, but already it has a rooting guide. The guide is posted over at Xda where you could possible get the root done in less than 5 minutes. I have used this guide on my phone, and it worked just fine for me.
Remember, be cautious of the inherent risks of this type of procedure. Follow the instructions carefully to avoid bricking your phone.
Check it: Xda-developers