Over the weekend, an intrepid XDA developer by the name of Kwiboo managed to corral version 4.0.1 of the Android Open Source Project — aka, Ice Cream Sandwich — into a custom ROM that works on the Nexus S. This means, if you have a Nexus S, a thrill-seeking personality, and about 10 minutes to spare, you can be running Ice Cream Sandwich in just a few screen taps.

The build isn’t perfect — there’s no video shooting, for example — but almost every major feature of ICS is available. Panorama mode works, for example (and yes, it’s as cool as you’d hoped), as do the updated Gmail, Google+, Music, and Maps apps. Face Unlock, data usage statistics, tethering — it all works. This build of ICS is completely usable — with one caveat: It’s simply not quite as smooth as the latest build of Gingerbread. 2D and 3D hardware acceleration works, so it’s not mega-slow, but it’s definitely not as fast as the finalized, official build of ICS that Google will distribute in the next few weeks.

How To Download Android 4.0 Ice Cream Sandwich It is important to download Android 4.0 Ice Cream Sandwich and rename the same as “update.zip” Connect your mobile to the PC using the data cable and move the zipped folder to the root directory on your mobile. The x86 Android* 4.0.4 (Ice Cream Sandwich) emulator system image enables you to run an emulation of Android on your development machine. In combination with the Android SDK, you can test out your Android applications on a virtual Android device based on Intel Architecture. Oct 19, 2011 - Are you a ROM developer? Just a solid geek with a passion for Android? After tonight's awesome Android 4.0 (Ice Cream Sandwich).

With that said, let’s dive in with some instructions. If you don’t have a Nexus S, or if you don’t want to play around with unofficial custom ROMs, there’s plenty of photos and screenshots further down. Update: We now have a hands-on video review of ICS running on the Nexus S.

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.

Update 27/11/2011: There’s now a third version of the custom ROM — and data usage limits are now working!

Update 28/11/2011: A stable and feature-complete alpha build of CyanogenMod 9 is now available, and you’re strongly recommended to use it instead of the custom ROM mentioned above.

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.

Ice Cream Sandwich Software Download

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.

At this point, check out our ICS explainer and hands-on tour so that you can find your way around the new OS — a lot has changed, and many features look completely different.

Please leave a comment if you discover a particularly cool feature, or if you have tips and tricks for installing custom ROMs.

1. Download the custom ROM

2. Root your phone and install ROM Manager

3. Make a backup!

Ice Cream Sandwich Software Download

4. Install Android 4 on your Nexus S

Android Ice Cream Sandwich Downloads