Nokia Developer Champion
Someone who does not work for Nokia but is recognised by them as an exceptional member of the developer community.
Nokia Developer Ambassador
Someone who works (usually part-time) for Nokia with a responsibility for helping people create apps.
Microsoft Valuable Professional (MVP)
Someone who does not work for Microsoft but is recognised by them as an exceptional member of the developer community
Microsoft Windows Phone Champion
Originally this term referred to people who work for Microsoft who could serve as a point of contact for people wanting help with Windows Phone development. This term is also now includes Windows Phone developer MVPs too.
I hope that's clear now.