A very old city friend coming across in conversation? (7)
I believe the answer is:
aurally
'coming across in conversation?' is the definition.
(aural means relating to hearing)
'a very old city friend' is the wordplay.
'very old city' becomes 'ur' (ancient Mesopotamian city).
'friend' becomes 'ally' ('ally' can be a synonym of 'friend').
'a'+'ur'+'ally'='AURALLY'
(Other definitions for aurally that I've seen before include "How one may learn" , "connected with hearing" , "Via the ear" .)