The phone remains in standby mode when placed horizontal. Yes, it apparently hovers like that when placed down. It's not magical, in any way. It has an electromagnet that allows the bulky end to shift weight. So probably that amazing device will stand up when there's a call. Nokia says that the user can tap the phone gently to make it recline back to its stand by mode to cancel a call (I believe the functionality will be implemented for a lot of tasks, like cancelling alarms). Anyway, the phone looks really, really beautiful.
Now that Nokia is ditching the Symbian operating system (and still there's no Android!), and going for MeeGo, it will surely run the phone on that OS, if it is finally decided that the phone be released commercially. Nokia says on its blog that the phone is just a concept, and the release of something like this hasn't been planned yet.
What I feel is (apart from it being a bulk in your pocket) the phone may turn out quite a hit, but won't become the highest selling Nokia device either. People nowadays look for the operating system instead of other things, and if Nokia doesn't put Android on it, it surely won't be that popular. I hope Nokia thinks about it.