According tot the Engadget, some owners of the Nexus One, unlocked, are receiving notifications to update to Android 2.2 Froyo. FRF85B. You can snag it from Google’s servers here, if you haven’t gotten the update notice yet. The best way to upgrade your Nexus One to the latest firmware build is to just check for it. Browse to Settings > About phone > System updates and you should receive a notification to download the update.
