No carrier or manufacturer support has been announced as of yet, but Canonical does mention in a video that there are some sort of deals or agreements with certain app and game developers to help push the app ecosystem for the OS.
Officially, the only compatible handset is the Galaxy Nexus. Canonical has several demo phones for the press in the UK according to The Verge (they even have a hands-on video). Very soon, they will start distributing demo images of the OS for developers to install and test out.
They seem to focus on content that has been recently used on the device and also on searching. The video shows at one point how the phone will know what you are looking for and it will search through the appropriate content on the web and on your phone.
Canonical is offering development kits that will allow developers to adapt webapps and HTML5 apps written for other platforms to run on Ubuntu very easily. Other than that, Ubuntu also allows developers to write native apps for the platform, which is necessary for apps with rich interfaces and heavy graphics, such as games. Ubuntu Software Center will also be available on mobile for distribution. This is most probably in addition to the ability to side-load apps from third-parties, similar to Android and OS X.
There are also some small animated demos of the features on the website that you can check out.
I can't wait to see what happens of this. Currently, they expect to see phones with Ubuntu release at some point in 2014. In my opinion, its success or failure all depends on whether the developer community comes out with a rich app ecosystem for this new-to-the-market OS.