Advertisement brought in these unusual phones? (7)
I believe the answer is:
headset
'phones?' is the definition.
(short for headphones)
'advertisement brought in these unusual' is the wordplay.
'advertisement' becomes 'ad' (synonyms).
'brought in' means one lot of letters goes inside another.
'unusual' indicates anagramming the letters.
'these' anagrammed gives 'heset'.
'ad' going within 'heset' is 'HEADSET'.
(Other definitions for headset that I've seen before include "Audio communication equipment worn by pilots, DJs etc" , "phones" , "Radio operator's equipt." , "Assistance for listener" , "One covers the ears" .)