In a fashion similar to the high-end graphics support, if we had been having a conversation about running unified communications or a VoIP session on a VDI desktop previously, I would have described it as kryptonite for VDI! It just didn't work.
The first call might have been acceptable; however, adding more users would ultimately result in resource-constrained servers that can no longer operate due to the amount of traffic generated. This would mean that the call experience would have been unusable.
However, all that has now changed, and you can now deploy a unified communications solution on your virtual desktop machines. There was always a great use case for this solution and VDI in, for example, a call center environment where you can deliver a DR solution or allow users to work from home if they are unable to make it to the office.