There is a feature of dail-in meeting services (like Meetingplace, webex meeting, etc) that allow the host to auto-mute everyone... sounds like your organization might want to use that feature.
Indeed, and in WebEx the host can auto-mute everyone, but then MUST tell people to unmute if they have a question, otherwise it is meeting #fail.
I've also had the opposite, where the host is UN-muting me, when I'm in the middle of eating my lunch during the meeting. I never got around to asking him WHY he wanted to hear me slurping my tea and crunching on my crisps (chips for the Americans).
I know, and I've thought about telling the people who set the call up to do that, but our seminars also have regular, legitimate questions. We could have a protocol where questions come through IMs, but that's cumbersome.