There is an active call More.
If you receive a call while already in a call, a message is displayed.
Depending on the mobile phone and mobile phone network provider you will hear a call-waiting sound.
In addition, in two phone mode you will hear an acoustic signal when the call goes through to the other (not yet active) mobile phone.
The incoming call is active.
If only one mobile phone is connected with the multimedia system, the previous call will be put on hold.
If during a call you accept a call with the other mobile phone when in two phone mode then the existing call is ended.
This function and behaviour depends on your mobile phone network provider and the mobile phone (see the manufacturer's operating instructions).