Mobile devices have gotten vastly more powerful just in the last couple of years, and the new quad-core smartphones likely to be announced soon have more powerful hardware than many people's desktops and laptops. For this reason, developers have been working to shoehorn Ubuntu Linux onto various devices of their choosing in order to release the hardware's full potential, but the hacked builds really don't do many phone's hardware justice.
Canonical, Ubuntu's parent company, announced last year that they would be bringing Ubuntu Linux to smartphones. At the time, we assumed that meant that a Ubuntu-powered device was in the works, but an unexpected part of the project was revealed in an unexpected announcement just this week.
As expected, it does concern Ubuntu running on mobile devices, just not in the way you might think. Instead of a version of Ubuntu to be used instead of an OS like Android, Canonical announced a version of the OS that runs alongside Android, and takes advantage of Android's core Linux kernel to run natively alongside the OS. By itself, your phone still acts as it normally would, but when docked and connected to a monitor and keyboard, you can use a full Ubuntu desktop powered directly by the phone's hardware.
This concept is very similar to what is used by the Motorola ATRIX, Droid RAZR MAXX, Bionic, and other devices in their laptop docks. Like Motorola's implementation, the customized Ubuntu desktop still allows you to take advantage of your device's functionality, such as calls, texts, and mobile data connectivity. You can even run your phone's applications within Ubuntu, they just open in a separate window.
All of your phone's data is also accessible through the Ubuntu interface, including things like contacts, calendar appointments, and documents. However, the Ubuntu interface includes productivity tools like Chrome and Firefox for browsing, VLC for media, Google Docs for document editing, the popular Thunderbird email client, and even the PiTiVi video editing suite.
While there are no compatible devices yet, all that a smartphone theoretically needs to support this kind of Ubuntu installation is Android version 2.3 Gingerbread or greater, hardware video acceleration, USB host mode, HDMI out, 512MB of RAM, and a dual-core processor. Obviously, more power will yield better results, but based on these specifications Ubuntu should run fine on nearly all current high-end phones.
You can't take advantage of it yet, but I really like where Canonical is going with their Ubuntu mobile project. Instead of trying to create something to replace Android and other mobile OSs, they are almost creating an application to run alongside them on the same device. In fact, Canonical CEO Mark Shuttleworth said that "The desktop is the killer-app for quad-core phones in 2012," and after seeing this I am inclined to think that he is right.[Ubuntu Official]