Call round for old and new pal (5)
I believe the answer is:
crony
'pal' is the definition.
(I know that pal can be written as crony)
'call round for old and new' is the wordplay.
'call' becomes 'cry' (as in a bird's call).
'round' means one lot of letters goes inside another.
'for old' becomes 'o' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'o'+'n'='on'
'cry' enclosing 'on' is 'CRONY'.
Can you help me to learn more?
(Other definitions for crony that I've seen before include "Corny (anag.)" , "Close companion" , "Sidekick" , "Close friend" , "mate" .)