Unattached princess's telephone line is busy? (10)
I believe the answer is:
disengaged
'unattached' is the definition.
(I've seen this before)
'line is busy?' is the wordplay.
'line' becomes 'dis' (I am not sure about this - if you are sure you should believe this answer much more).
'is busy?' becomes 'engaged' (similar in meaning).
'dis'+'engaged'='DISENGAGED'
'princess's telephone' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for disengaged that I've seen before include "Detached, separated" , "withdrawn" , "Unattached" .)