We use VoIP internally for our telephone system and I think the technology is great. However, all the hype that has built up around the technology in the public domain is, from the point of view of the corporate, irrelevant.
Guy Kewney writes well on the lack of interoperability of the various players and suggests that their interest is in generating advertising revenue. The same issue has long plagued the instant messaging clients, although this has begun to change. I wonder if eBay’s purchase of Skype will put any momentum behind VoIP interoperability.