If you are on a modded Nexus One, with either a root on the stock Android 2.1, or with theHTC Desire ROM and are too lazy to return to stock to receive the OTA update, this method is for you. As a pre-requisite, you will need to have an unlocked bootloader, and root access on your Nexus One. You will also need to have the patched recovery-RA-nexus-v1.5.3.img recoveryon your N1.
If you meet all the pre-requisite requirements, then this guide is for you. Follow the instructions posted below to install Android 2.2 Froyo on your modded Nexus One.
NOTE: If you are on a stock Android 2.1 waiting for OTA update to receive, follow the instructions posted here to manually install the update now!
Step 1: Download the rooted Android 2.2 Froyo (FRF50) from the source link here and copy it to over to the root of the SD card on the phone.
Step 2: Now power off the phone and enter the recovery image by powering on while pressing the ‘Home’ trackball.
select “BOOTLOADER” –> “RECOVERY”
Step 3: Now you will be rebooted into custom RA recovery mode. Select ‘Backup/Restore’ from the menu to do a Nandroid backup.
Step 4: Now select “Flash zip from sdcard” to flash your Nexus One with this latest (already) rooted Android 2.2 Froyo FRF50 ROM.
Step 5: Do a complete wipe by selecting the “Wipe” option as seen in the screenshot above.
Step 6: Reboot your phone! Voila, you now have the rooted Android 2.2 ROM on your Nexus One!