Call to allow twisted lock (7)
I believe the answer is:
ringlet
'twisted lock' is the definition.
'call to allow' is the wordplay.
'call' becomes 'ring' (telephone call).
'to allow' becomes 'let' ('let' can be a synonym of 'allow').
'ring'+'let'='RINGLET'
(Other definitions for ringlet that I've seen before include "Little curl" , "Cluster of hair" , "twist of sorts?" , "hair styling" , "Curl or tendril" .)