The only* way to do client-less Lync in the browser is with UCWA. Right now,UCWA is only IM/P but voice/video is coming by the end of the year. Everything else (apart from Lync Web Access obv) requires the client to be on the machine.
*you could write a web proxy to a UCMA service you've written which would achieve the same thing,but this wouldn't be able to do voice/video either.