I haven't been in one myself, but video conference protest hearings have been held. US Sailing even has (or at least had) a GoToMeeting account available for that purpose. The judges I've spoken to who have done it feel that it's very important to be able to see the protestor and protestee (as well as the witnesses). It's important to get the nonverbal clues, as well as to insure that the parties aren't getting off-camera advice.
I've signed up as "judge on call" for a couple of events, but wasn't needed to phone into a hearing.
I've attended a few regattas where I couldn't be on protest committee (conflict of interest as a competitor), but I've offered advice to the PC. I can't hear testimony, question witnesses, help deliberate, or otherwise participate, but I can be called as a witness to advise on protest procedures and rule application.
