Conference Call
When two calls are in progress (one active and one on
hold), press and hold the 
button
until you hear a
double beep indicating that the two calls have been
joined into one conference call.
See also:
Using ACC On Hills
When driving on hills, ACC may not detect a vehicle in
your lane. Depending on the speed, vehicle load, traffic
conditions, and the steepness of the hills, ACC performance
may be limited.
...
Conference Call
When two calls are in progress (one active and one on hold), press and hold the
button until you hear a double beep
indicating that the two calls have been joined into one conference call. ...
Toggling Between Calls
If two calls are in progress (one active and one on hold),
press the button until you hear a
single beep,
indicating that the active and hold status of the two calls
have switched. Only one c ...