Restricted revision to one working - that's a rare thing (7,7)
I believe the answer is:
limited edition
'a rare thing' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'restricted revision to one working' is the wordplay.
I cannot really see how this works, but
'restricted' could be 'limited' ('limit' can be a synonym of 'restrict') and 'limited' is present in the answer.
'revision' could be 'edit' (I've seen this in another clue) and 'edit' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
'working' could be 'on' (on can mean working or activated) and 'on' is present in the answer.
No letters remain.
This explanation may well be incorrect...
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for limited edition that I've seen before include "Small number of copies" , "An issue of a fixed number" , "Rare book" .)