A circuit and method is described enabling a telephone having two or more lines to have the capability of initiating two simultaneous calls, where there is two-way communication on one of the calls (the collaborating call"), and active monitoring of the second call (the "teleconference"). A router is used so that the outbound audio signal of the user can easily be switched between the teleconference and the collaborating call. At all times, the transmit path of one of the calls is muted to ensure privacy of the other call.