well..I'm not directly working on my CCVP yet. But I am seeing a demand for voip engineers coming to my company in a rather short timeframe. In fact we recently lost one of our engineers to an outsourcing company to become a voice engineer. Last I had talked to him and heard through the grapevine, he's been spending his first few months studying up, and part of the deal was for him to get his CCVP.
Picking one vendor's certs over another I think is a personal choice. But having both could be beneficial.