Files and instructions available to run both operating systems on your Nexus 4
If you're looking to have a little bit of Ubuntu fun on your Nexus 4 during the holiday break, Canonical has something that should interest you. They have released a method to flash your phone so that it can boot into Ubuntu from Android, and boot back to "normal" using what looks and acts like normal applications to the end user.
Looking through the instructions, you'll need to be running Ubuntu on your home computer and know your way around the command line. It's all scripted so there is little room for error, and the only path back is a full wipe and reflash of the factory images. You'll also need to flash an old radio if you want to make phone calls on the Ubuntu side, using a Jelly Bean factory image.
While this isn't for everybody — and is clearly marked as a developer preview — it is a good way to have a look at how Ubuntu is progressing and still be able to revert back to something more familiar for those times when you need it. Follow the link below, and read everything, if you're interested.
Source: Ubuntu Developer Portal