You can add parties to an existing conference.

1.Press Conf to put the conference on hold. This does not affect the other conference parties who can continue talking to each other.
2.Press an available appearance key on which to make a call.
3.Dial the party that you want to add to the conference.
4.If they answer and want to join the call, press Conf again.
5.If they do not want to join the call or do not answer, press Drop and then press the appearance key of the held call.