Page or intercom to phones without auto-answer

I’m trying to make simultaneous calls to serveral SIP phones via the PAGE command. The phones ring shortly, but the 180 ringing is followed directly by a CANCEL from Asterisk. I believe that phones which support auto-answer will probably skip the 180 ringing an directly send 200 ok, but that’s not what I need : the phones should ring as long as they are not answered, and only those that answer should be connected to the caller (one direction or both-way depending option), while the others keep on ringing.

So this is not really a PAGE application, but rather some kind of intercom or pre-programmed conference.

An alternative approach could be to simultaneously call the phones via QUEUE or DIAL commands, and when they answer to put them in a specific conference bridge, but I don’t know how to realize this - is it possible to add users upon answering in a specific conference ?

I would really appriciate some advise or hint to realize this.