What I gathered after reading the official site in the link above is that you can install or rather dual boot Ubuntu into Android 2.3 (Gingerbread) and above.
When using it as a mobile phone, you will use your Android phone per normal. However, when you connect the phone to a monitor through HDMI and a keyboard/mouse through USB Host mode, the Ubuntu OS within Android boots and you can use it like a normal PC.
According to the features, when your phone is connected, you can answer calls, reply to SMSes all within the Ubuntu itself without the need to touch your phone.
Of course, having to dual boot two OSes requires high hardware requirements and hence you need to have at least a dual core 1GHz Android phone with at least 512MB of RAM.
Ubuntu for Android provides a full desktop experience, including office software, web browsing, email and media applications, on Android phones docked to a screen and keyboard. Thanks to tight integration with the Android service layer, the transition between the two environments is seamless, making it easy to access the phone’s services from the desktop when docked.
Ubuntu for Android requires minimal custom hardware enablement, allowing fast and cost-efficient core integration. It requires a core based on Android 2.3 (Gingerbread) or any subsequent version.
Ubuntu and Android share the same kernel. When docked, the Ubuntu OS boots and runs concurrently with Android. This allows both mobile and desktop functionality to co-exist in different runtimes.
Shared services and applications are delivered using a Convergence API module which ensures the tight integration between desktop and mobile environments. Work is balanced across the cores of the phone. When the handset is not docked, both CPU cores transfer their full power to Android.
- Dual-core 1GHz CPU
- 512 MB RAM
- Video acceleration: shared kernel driver with associated X driver;Open GL, ES/EGL
- Storage: 2GB for OS disk image
- HDMI: video out with secondary frame buffer device
- USB host mode