According to Canonical, "Images and open source code for the Touch Developer Preview of Ubuntu will be published on Thursday 21st February, supporting the Galaxy Nexus and Nexus 4 smartphones."
This version, while it will be bootable, isn't suitable for casual users. It's "intended for enthusiasts and developers, to familiarize themselves with Ubuntu's smartphone experience and develop applications on spare handsets. Tools that manage the flashing of the phone will be available on the same day in the Ubuntu archives, making it easy to keep a device up to date with the latest version of the Touch Developer Preview."
If you happen to be at the Mobile World Congress (MWC) in Barcelona in late February you can have you phones flashed to Ubuntu by Canonical team members at the Ubuntu stand, booth number 81D30, App Planet Hall 8.1, where Ubuntu will be shown on a range of devices.
Of course, this code release is primarily for Ubuntu developers. In addition, while it's going to be released for the Nexus smartphone line, Canonical also asserts that it will enable "developers to port the platform to other devices. Our platform supports a wide range of screen sizes and resolutions. Developers who have experience bringing up phone environments will find it relatively easy to port Ubuntu to current handsets" said Pat McGowan, who leads the Ubuntu phone integration effort in a statement. "We look forward to adding support for additional devices for everyday testing and experimentation."
Canonical's goal is for there to be one common version of Ubuntu that "will deliver a mobile, tablet, desktop or TV experiences depending on the device it is installed on, or where it is docked. Ubuntu 13.10 (due in October) will include a complete entry-level smartphone experience."
Canonical has published a mobile Ubuntu Preview software development kit (SDK) and App Design Guides to allow developers to create applications for the full range of Ubuntu platforms. The toolkit provides a range of documented templates to enable native applications to be created quickly and easily. These use QML (Qt Meta Language) widgets, on top of HTML5 and OpenGL for quick interface development.
The App Design Guides explain how these templates can be used to design and build beautiful and usable apps. The end result, Canonical promises, is an operating system where "Developers will not need to cross-compile or package applications differently for phone, tablet, PC and TV. One platform serves all four, a single application binary can do the same"
"This release marks the threshold of wider engagement -- both with industry and community," said Mark Shuttleworth, founder of Ubuntu, in a statement. "For developers, contributors and partners, there is now a coherent experience that warrants attention. The cleanest, most stylish mobile interface around."