Naughty ad by telephone not acceptable (6,3,4)
I believe the answer is:
beyond the pale
'acceptable' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'naughty ad by telephone' is the wordplay.
'naughty' indicates anagramming the letters.
'ad'+'by'+'telephone'='adbytelephone'
'adbytelephone' with letters rearranged gives 'BEYOND THE PALE'.
'not' is the link.
Can you help me to learn more?
(Other definitions for beyond the pale that I've seen before include "Totally unacceptable" , "Outside limits of social convention" , "Morally or socially intolerable" , "Outside the bounds of acceptable behaviour" , "Socially unacceptable" .)