Popular expression around firm for a means of contacting others (8)

I believe the answer is:

intercom

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'a means of contacting others' is the definition.
I can't tell whether this defines the answer.

'popular expression around firm' is the wordplay.
'popular' becomes 'in' (something that's 'in' is fashionable).
'expression' becomes 'term' (both can mean a piece of vocabulary).
'around' indicates putting letters inside.
'firm' becomes 'co' (abbreviation for company).
'term' going around 'co' is 'tercom'.
'in'+'tercom'='INTERCOM'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for intercom that I've seen before include "Device for two-way talking" , "communications system" , "Two-way speaking device" , "Means of transmitting messages" , "Speaker system" .)

I've seen this clue in The Guardian.

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