Citroen beginning to make mobile phone system (8)
I believe the answer is:
intercom
'phone system' is the definition.
'intercom' can be an answer for 'system' (intercom is a kind of system). I'm unsure of the 'phone' bit.
'citroen beginning to make mobile' is the wordplay.
'beginning to' says to take the initial letters.
'mobile' indicates anagramming the letters.
The first letter of 'make' is 'm'.
'citroen'+'m'='citroenm'
'citroenm' with letters rearranged gives 'INTERCOM'.
Can you help me to learn more?
(Other definitions for intercom that I've seen before include "Two-way speaking device" , "System of communication often on door" , "short range phone" , "System of communication by radio or telephone" , "Communications device" .)