I'm not going to get into a contest on who knows more about conferencing, nor am I disputing that a single line telephone can participate in a six party conference. All I asked was if you had ever tried to instruct someone who is typically not telephone savvy on setting up that type of conference. Or, more correctly, instructed all three parties required in how to set up that type of conference. Simple question.
Also, after expending half a Twinkie's worth of brain power I deduced that you could indeed create a six party conference on a digital set and then transfer the call into a single line telephone because as soon as you hit that transfer button you are placing the other five parties on hold, grabbing an idle line and sending the five parties to the new sixth party analog phone as you yourself drop off the call. Presto, chango, easy six party conference set up by an assistant who now looks like Einstein to the folks in the conference room.
Ironically none of this is really relevant to the question mikej asked because he only needed to create a three party conference according to his scenario.