Seems like this was sort of downplayed...getting only a quick mention...because I'm sure the carriers aren't crazy about this. Makes it even more convenient to stay with my T-mobile $30 plan with only 100 minutes.
I don't see how carriers would justify refusing to allow this on 3G/4G when they now allow video FaceTime calls on data. Seems like Apple played this smart. Introduce it as video only...eventually get the carriers to agree to allow it to be used by telling them that customers will use more and pay for more data, then add a voice only feature afterwards!