Brief garage worker on message with procedures (10)

'procedures' is the definition.
The definition and answer can be both acts as well as being plural nouns.
Perhaps there's an association between them I don't understand?

'brief garage worker on message with' is the wordplay.
'brief' means to remove the last letter.
'garage worker' becomes 'mechanic' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'message with' becomes 'sms' (I can't explain this - if you can you should believe this answer much more).
'mechanic' with its final letter taken away is 'mechani'.
'mechani'+'sms'='MECHANISMS'

Can you help me to learn more?