Have a go at short-term worker engaged by US telecom giant (7)
I believe the answer is:
attempt
'have a go at' is the definition.
'short-term worker engaged by us telecom giant' is the wordplay.
'short-term worker' becomes 'temp' (I've seen this before).
'engaged by' is an insertion indicator (I've seen this in other clues).
'us telecom giant' becomes 'att' (Us firm AT and T).
'temp' going inside 'att' is 'ATTEMPT'.
(Other definitions for attempt that I've seen before include "Tackle" , "Essay" , "Try to climb (a peak)" , "Try, make an effort" , "bash" .)