Hanging up or not having yet hung up (2,3,4)
I believe the answer is:
on the line
'yet hung up' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'hanging up or not' is the wordplay.
I cannot quite see how this works, but
an anagram of 'not' is 'ont' which is located in the answer.
This explanation may well be incorrect...
'having' is the link.
Can you help me to learn more?
(Other definitions for on the line that I've seen before include "At serious risk" , "At risk - or speaking on telephone" , "Caller may be" , "Using the phone" , "when one is at risk" .)