You can now enabling multitouch and fixing T-Mobile 3G issue, check step by step bellow:
- Download the update file ROM from Google official web link at here.
- Rename the file you just downloaded to update.zip and copy it onto your microSD card.
- Turn your Nexus One off, after that, hold down the trackball and press the power button.
- You will booted into a white screen with three Android robots on skateboards. Please select “Bootloader” to continue.
- On the next screen, select “Recovery”
- Your phone will reboot, giving you a picture of the Android robot and an exclamation point inside a triangle.
- Now press the power button and volume up button at the same time. It could take a couple of tries.
- Now choose “Apply sdcard:update.zip” and let things run their course.