Finally, when telephone call is on hold (6)
I believe the answer is:
nelson
'hold' is the definition.
(wrestling hold)
'finally when telephone call is on' is the wordplay.
'finally' suggests the final letters.
The last letters of 'when telephone call is' are 'nels'.
'nels'+'on'='NELSON'
(Other definitions for nelson that I've seen before include "British naval hero" , "'Horatio ..., English admiral (6)'" , "one visibly affected by fighting" , "Horatio - - , naval commander" , "Horatio ..., British admiral" .)