Fast telephoto lens for m4/3?

Hi, I am probaly going to buy a GH2 once it comes out. I need a fast telephoto or zoom lens, but as zoom lenses are more expensive I guess a prime would be the best solution.

So I was looking at lenses for m4/3 and didn't see a single fast long lens. In 4/3 lenses Sigma has for instance the 150mm f2.8 but it doesn't have OIS, who knows when the new version will hit the stores and what it will cost. I'm not even sure how compatible it is with the GH2.

Any suggestions please?