Hi @Edwin Blankson-Mills,
''If the called person has the Call Waiting feature enabled'', there is no setting in the caller’s phone that will tell the caller that the called person is on another call .
The caller will get the ringtone signal until the called person either answers the call, declines the call or it is switched to the called person’s voicemail service after the selected ringing period has elapsed (as setup by the called person).
I''f the called person doesn’t have the Call waiting feature enabled'' the caller will get the busy signal if the phone is in use.
''Call Waiting'' is not there for the benefit of the calling person to know if the called phone is in use or not. ''It is a feature provided on the'' '''called person’s phone service'''.
After all it is ''their'' phone service and they should be able to decide how they want to use their phone and whether they want to answer another call or not.
There is no way of knowing whether the called phone is in use or just not being answered or if it is a landline service whether the line is faulty and the called phone is not ringing anyway.