You can select to have internal calls automatically connected if you are not already on a call. The call is connected after the phone gives a brief tone, using either the phone's speaker or the headset as set by the phone's audio path setting.
This function can be assigned to a feature button configured with the Auto Answer action. The button lamp indicates when 'internal auto answer' is on. See Programmable Feature Buttons.
To do this during a call, press the PHONE key and then press Features.