I'm almost 100% sure it is not supported, and I'm certain it's not recommended. If you look at their "best practices", you'll see they use a ton of servers (10, 15?) for all different roles. Our own implementation is only for 200 users and has 3 servers, one edge server, one cwa and one front server. This was the minimum we had to use for our infrastructure.
I'm sure text would work fine if virtualized, but voice/video would become a problem rather fast I reckon.
Microsoft released a pretty good white paper on it called Running Microsoft Office Communications Server 2007 R2 in a Virtualized Topology. The gist is some roles you can virtualise no problems, but for those Voice, audio/video, Web conferencing, and application sharing roles you need to stick to physical boxes.
I'm almost 100% sure it is not supported, and I'm certain it's not recommended. If you look at their "best practices", you'll see they use a ton of servers (10, 15?) for all different roles. Our own implementation is only for 200 users and has 3 servers, one edge server, one cwa and one front server. This was the minimum we had to use for our infrastructure.
I'm sure text would work fine if virtualized, but voice/video would become a problem rather fast I reckon.