Call to allow a lock of hair (7)
I believe the answer is:
ringlet
'a lock of hair' is the definition.
(I've seen this before)
'call to allow' is the wordplay.
'call' becomes 'ring' (telephone call).
'to allow' becomes 'let' (synonyms).
'ring'+'let'='RINGLET'
(Other definitions for ringlet that I've seen before include "Little curl" , "Curl of hair; butterfly" , "Hair curl, of an Irish dancer perhaps" , "Long curl of hair" , "twist of sorts?" .)