sources close to Google that cannot be named confirm that e.g. Samsung or HTC paid nothing to Microsoft. or rather got all license fees back in terms of Windows Phone marketing kickbacks
I personally believe this to be true, it's how Microsoft often does these things and the fact that a bookstore stood up to them and won makes me think the agreements with Samsung etc. are more about showmanship.
But I've never seen this side of the story repeated anywhere with quotes from sources, even anonymous ones.