Long video, but right from the beginning you see the phone and how the modules work. Pretty cool.
there will be three sizes at launch: a mini, which looks to be about the size of an iPhone; medium, which is probably a "standard" Android phone size of 4.7ish inches (that's a guess); and a larger, phablet-esque size that is approximately one-third larger than the medium endo. The best part about the three is that all modules will be completely interchangeable between them, so you could theoretically have all three endos and switch your phone size from day-to-day.
Google's goal is to keep Ara – which is noted to be called Google Ara in the video – as affordable as possible. The endoskeletons (which are the base of the entire phone) should run about $15 a piece since they don't do much outside of allowing all the other components to talk to one another; modules, of course, will vary in pricing but are still said to be "affordable."
April 15-16 will be a Project Ara Developers Conference (at the Google-plex and via Online). Will have Project Ara phones in developer hands later this year and in concumer hands by Jan 2015.