Follow old reserves with German military ID (3,3)
I believe the answer is:
dog tag
'military id' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'follow old reserves with german' is the wordplay.
'follow' becomes 'dog' (dog can mean to follow or torment).
'old reserves' becomes 'ta' (Territorial Army, army reserves. I am not sure about the 'old' bit.).
'with' says to put letters next to each other.
'german' becomes 'g' (abbreviation).
'dog'+'ta'+'g'='DOG TAG'
Can you help me to learn more?
(Other definitions for dog tag that I've seen before include "source of information on GI" , "Pet identifier" , "US soldier's metal identity disk" , "Canine ID" .)