Well, easy GPO source is a business listing (6,5)
I believe the answer is:
yellow pages
'a business listing' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'well easy gpo source' is the wordplay.
'well easy gpo' can be anagrammed to 'YELLOW PAGES'.
But, I'm unsure how this is indicated.
'is' is the link.
Can you help me to learn more?
(Other definitions for yellow pages that I've seen before include "looking for service here?" , "Directory" , "Reference book for business numbers" , "Telephone reference book" .)