Lync phone edition has an option to Consult then transfer to. The Attendant has a button for this as well, as well as the ability to hit CTRL+L to achieve the same thing. Microsoft decided to leave this button out of the Lync PC client. It was in the OCS client but not in Lync. I know callers can merge calls using "Current conversation", but a Consult then transfer to button would be so much easier.