Device her postman misdirected (10)
I believe the answer is:
smartphone
'device' is the definition.
(I have seen 'Clever device' mean 'smartphone' so perhaps 'device' could also mean 'smartphone')
'her postman misdirected' is the wordplay.
'misdirected' indicates anagramming the letters (I've seen this in other clues).
'her'+'postman'='herpostman'
'herpostman' anagrammed gives 'SMARTPHONE'.
(Other definitions for smartphone that I've seen before include "Clever device" , "Multi-purpose mobile device" , "Advanced electronic hand-held device" .)