Just curious, is a user supposed to put the device up to their ear to make a phone call? Or is the expectation to use a bluetooth headset?
I'm not being anti-microsoft, but it looks like someone just brought back the netbook.
It's now a "feature" that primarily caters to power users: if you use calling, you use it a lot - otherwise the user tends to use messaging / texting / other medium (like FaceTime.)
Therefore my design guess is that Microsoft is aiming for the video call / bluetooth headset, and will take the hit in terms of awkwardness for holding up to your ear for some calls.