Old long-distance communication could be a trumpet (5,4)
I believe the answer is:
trunk call
'old long-distance' is the definition.
'trunk call' can be an answer for 'long-distance' (synonyms). I'm not certain of the 'old' bit.
'communication could be a trumpet' is the wordplay.
I cannot really understand how this works, but
'communication' could be 'call' (call is a kind of communication) and 'call' is found within the answer.
'be' could be 'run' (running is a kind of being) and 'run' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for trunk call that I've seen before include "Communication at a distance" , "peculiar to India and Africa?" , "Old communication" .)