One of the numbers for church service
I believe the answer is:
air force
'service' is the definition.
(air force is a kind of service)
'one of the numbers for church' is the wordplay.
'one of the numbers' becomes 'air' (I can't explain this - if you can you should give a lot more credence to this answer).
'church' becomes 'ce' (abbreviation for Church of England).
'air'+'for'+'ce'='AIR FORCE'
Can you help me to learn more?
(Other definitions for air force that I've seen before include "Armed service" , "Simple tune for church service" , "Kind of blue" , "Junior service" , "Country's military planes" .)