The call ended abruptly.
( ( The call ) ( ( ended abruptly ) . ) )
(ROOT (S (NP (DT The) (NN call)) (VP (VBD ended) (ADVP (RB abruptly))) (. .)))
The call ended without warning. 
( ( The call ) ( ( ended ( without warning ) ) . ) )
(ROOT (S (NP (DT The) (NN call)) (VP (VBD ended) (PP (IN without) (NP (NN warning)))) (. .)))