1. Download the custom ROM
Hit up XDA-Developers and download the Nexus S custom ROM (v2, “no need for wifi patch”). If you have a 4G Nexus S, you can download the appropriate custom ROM, but we haven’t tested it — so be careful.
Once the zip file is downloaded, transfer it to your phone’s SD card.
2. Root your phone and install ROM Manager
If you’re already using CyanogenMod (which hopefully you are), your phone will already be rooted and have ROM Manager installed. Otherwise, you’re going to have to root your phone. This isn’t particularly hard, but it is a multi-step process, and there’s a risk that you could brick your Nexus S. The best way to do this is to follow a video guide, but googling for “how to root nexus s” works as well.
With ROM Manager installed, open it up and make sure the latest version of the ClockworkMod recovery image is installed (“Flash Clockwork Mod Recovery” — see right).
3. Make a backup!
Scroll down in ROM Manager and select “Backup Current ROM.” This will back up all of the system and app data on your phone — but not any data on your SD card, such as photos or music. This backup is saved on your phone’s SD card, in the “clockworkmod” directory — and once it’s done, you should copy this to your computer via USB. You will need this backup if you want to restore your phone to its pre-ICS state.
Installing ICS on your Nexus S should not affect the contents of your SD card, but it’s always wise to make a copy of your photos and videos, just in case. To do so, plug your phone into a computer and transfer the files via USB.
Please bear in mind that installing this build of ICS will completely wipe out your installed apps.You can reinstall them, but you will lose all of your settings. You shouldn’t proceed unless you really want to try out Ice Cream Sandwich. Remember, though, that you should be able to restore your backup without issue — so you do have a way out.
4. Install Android 4 on your Nexus S
Now, from ROM Manager, hit “Install ROM from SD Card,” and surf to the zip file on your SD card (“ics-crespo-aosp-4.0.1-v2-unsigned.zip” or similar). Select “Wipe Data and Cache” and “Wipe Dalvik Cache” from the menu and press OK (see right).
ICS will now install. Your phone will reboot, and in about 60 seconds you’ll be greeted by Ice Cream Sandwich’s phone setup screens, and then some basic tutorials.
Welcome to Ice Cream Sandwich! This build is pre-rooted, so to revert to Gingerbread you will simply have to re-install ROM Manager and restore your backup..
国内rom传送: