Important frontier penetrated by a communicator on line (10)
I believe the answer is:
keyboarder
'communicator on line' is the definition.
I know nothing about this answer so I can't judge whether this works.
'important frontier penetrated by a' is the wordplay.
'important' becomes 'key' (similar in meaning).
'frontier' becomes 'border' (I've seen this before).
'penetrated by' indicates putting letters inside (I've seen this in other clues).
'border' placed around 'a' is 'boarder'.
'key'+'boarder'='KEYBOARDER'
Can you help me to learn more?
(Another definition for keyboarder that I've seen is " one typing text".)