Sucker is about to call shortly (6)
I believe the answer is:
siphon
'sucker' is the definition.
'about to call shortly' is the wordplay.
'about' becomes 'si' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to call' becomes 'phone' ('phone' can be a synonym of 'call').
'shortly' means to remove the last letter.
'phone' with its final letter taken away is 'phon'.
'si'+'phon'='SIPHON'
'is' is the link.
(Other definitions for siphon that I've seen before include "Tube drawing off liquid" , "Tube used to draw a liquid" , "Tube down which liquid flows unaided" , "A bottle that squirts, say soda water" , "Tube taking fluid from higher to lower point" .)