This is a bit old – but if you have not seen this already go check out:

http://www.microsoft.com/Mediaroom/PR/VirtualizationPR.aspx

The summary is that we have launched Microsoft Mediaroom with virtualization to enable IPTV providers to reduce their costs by consolidating hardware and increasing utilization with Hyper-V.

The neat thing about this – from my point of view – is that it demonstrates that Hyper-V is fully capable of handling such a demanding work load.  I also have heard from customers who are running their corporate VoIP servers in Hyper-V quite happily.

Cheers,
Ben