They might not be to some non-tech-savy people... If you don't understand the concept of a virtual button that thing might just look like a rounded, blue rectangle with text in it. Nothing hints that it is supposed to be touched, it might as well just be some kind of highlighting.
The only exception I can think of is that it's obviously a button if it uses system controls.
Those are a thousand times better than "buttons" that are just underlined text.
I'm no UI pro but there's one thing I'm confident in saying through my experience and it's that you can't be certain something is intuitive until you've tried it on real people in a real scenario.
Your example button is fine with me but I feeling like it's the sort of thing that would confuse my mother. Acceptable depending on your app but I'm guessing that's Skype or similar and the 60+ market is probably important for them. But maybe I'm wrong, test test test.
Lots of websites use that little pill shape for other things.
A button should announce that it is clickable, while the rest of the UI isn't. Just because something has a different background and shape doesn't tell me it's clickable.