Canonical has released the Ubuntu Touch Development Preview for a few select devices and installing it is quite easy. This a tutorial that will show how you can return from your Ubuntu for Phones OS back to the Android system that previously inhabited the device.
Even if the installation of Ubuntu Touch Development Preview is easier than a stroll in the park, as described by our previous tutorial, restoring your Android operating system proves to be even easier.
If you remembered our advice and you saved the build number of your device (for convenience we'll use the one needed for our phone, JDQ39), you will know what to look for.
We installed Ubuntu Touch Development Preview on an LG Nexus 4, so we had to locate the appropriate version from the official Google website (Factory Images for Nexus Devices).
Keep in mind that this tutorial applies to all the supported Nexus devices: Galaxy Nexus (maguro), Nexus 4 (mako), Nexus 7 (grouper), and Nexus 10 (manta).
After you've downloaded the official factory image from Google, you will need to extract it. If you are doing this on a different system from the one you used to flash the Ubuntu OS, you are going to have to install the Touch Developer Preview Tools, via PPA (Precise, Quantal and Raring support).
Just enter the following commands in order to install the tools:
sudo add-apt-repository ppa:phablet-team/tools
sudo apt-get update
sudo apt-get install phablet-tools android-tools-adb android-tools-fastboot
Having installed the tools, just navigate to the folder in which you have extracted the Android image files and enter the following commands:
sudo adb reboot-bootloader
Just sit back and let the tools do their job. After the process is finished, the phone should boot into Android.
The Ubuntu Touch Developer Preview is intended to be used for development and evaluation purposes only. It does not provide all of the features and services of a retail phone and cannot replace your current handset.