Is this basically a broadcast / lecture, where all users are muted and only listen to the administrator's speech? Or is it a real conference, where users can ask questions, vote on issues and make comments?
For the latter, Asterisk is IMO unsuitable for meetings with more than half a dozen participants. There are many commercial services, ranging from free to pricey, that allow you to conduct an orderly meeting. The administrator has a web-based interface that allows him to see who is talking, identify and mute unwanted noise sources, see who has silently "raised their hand", etc. The system maintains a Q&A queue and can automatically unmute questioners in turn. Participants who are unruly, or have technical problems with echo or noise can be dropped from the conference. Speaker information can automatically annotate the conference recording and transcription, so you can be sure of who said what.
Though there are many others, you might start by looking at
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www.freeconferencecallhd.com/»
www.turbobridge.com/»
www.zipdx.info/How will multiple participants at a given location be handled? A $20 speakerphone won't cut it. A Polycom SoundStation or similar is good for up to about eight people. With extension mics, maybe 15. Beyond that, you'll need a professionally installed system.
The enhancements you are requesting would entail quite a bit of scripting. If you want to do this yourself, you might start by looking at the existing source code for conferences, IVR, speaking clock, etc. If you'd rather find a pro to do it, post at »
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I don't know whether this fits your model, but a simpler alternative is to create a web page where users could register and state their phone number and the number of participants. When the form is submitted, they would be given a PIN to access the FreePBX or commercial conference as a normal user. The administrator would just dial in and give the admin PIN.