Call service for something to blow (4)

I believe the answer is:

horn

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'something to blow' is the definition.
I can't judge whether this definition defines the answer.

'call service' is the wordplay.
'call' becomes 'ho' (historical exclamation used to attract attention).
'service' becomes 'RN' (abbreviation for Royal Navy).
'ho'+'rn'='HORN'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for horn that I've seen before include "Bony outgrowth on an animal" , "Head appendage; warning instrument" , "Brass musical instrument" , "Instrument - rhino's feature" , "Wind instrument - cape" .)

I've seen this clue in the Sydney Morning Herald.

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