Caller took a long time to connect pair (5)
I believe the answer is:
pager
'caller took a long' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'time to connect pair' is the wordplay.
I cannot quite understand how this works, but
'time' could be 'age' (an age is a period of time) and 'age' is found within the answer.
'pair' could be 'pr' (abbreviation) and 'pr' is present in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for pager that I've seen before include "communicator?" , "Small radio bleeper for contact" , "Bleeper device" , "Old electronic bleeping device" , "Way to contact" .)