Really? How many users would want a phone interface that looks like Ubuntu desktop? And from what I saw in the video it doesn't, so that pretty much negates the concept of having one OS platform for many device types.
What would you see as the advantages of running this versus Android? Google probably wouldn't allow it to access the thousands of apps in the Play Store or their services like Google Voice and Google+ except from the browser interfaces for those apps.
After all the effort that went into getting MMS for VM working on AOSP based ROM's, imagine the issues in getting all the apps used on a daily basis ported over and working on another OS, and it would take a lot of resources to accomplish that. With Apple, Google and Microsoft as the major players in the mobile phone market, can a company like Canonical really compete?
IMO, Ubuntu has a better chance of succeeding on tablets, and should try to get a foothold there first. Here's the vendor's webpage for the phone version of Ubuntu
and I don't see any specifications on hardware requirements, but with enough effort it could probably be ported to run on most devices that can support Jelly Bean.
My guess is that this will be pretty much of a novelty on phones, but I could be wrong. I just don't see any problems with the current phone OS's that it solves.