The following is a step by step guide to root the samsung Galaxy S 2 from T-Mobile. I have tried it and it worked for me on Android 2.3.6. It's the fastest and safest method to root the phone as far as i know.
- Download the root files from here. And extract it to desktop.
- Make sure there's a micro-sd card in the phone.
- Connect the T-Mobile Galaxy S2 to PC via USB port. Mount it as USB mass storage.
- Copy the su-3.0.5-efgh-signed.zip to phone's sd card.
- Reboot the phone into download mode (Hold both volume keys and then connect to PC with USB cable).
- Connect the phone to PC via USB.
- Start the included odin software, check PDA and choose the recovery-cwm-hercules.tar.
- Click Start. Now it will install the CWM Recovery and reboot the phone after it's done.
- Reboot the phone into recovery mode.
- Go to CWM Recovery menu and choose install zip from sd card. Now select the su-3.0.5-efgh-signed.zip.
- Reboot the phone after it's now. Congratulations! Now your phone is rooted!
Did it work for you? Please leave a comment if you run into any issues or this is helpful.