Trout, 20, was batting .403 with five triples and six stolen bases in 77 at-bats for Triple-A Salt Lake.
The Angels, picked by many to reach the World Series after signing Albert Pujols and C.J. Wilson, are off to a 6-14 start and dealing with a glut of corner infielders and designated hitters for limited at-bats.
Abreu, 38, had gotten just 24 at-bats in the first three weeks and was batting .208. The Angels thought they had come close to trading Abreu twice, first to the New York Yankees and then to the Cleveland Indians. Abreu grumbled publicly a couple of times about his limited role.
Abreu signed with the Angels before the 2009 season. He appeared in 456 games for them and batted .267 with 43 home runs and 246 RBIs. The two-time All-Star is one of four players all-time with at least 500 doubles, 250 home runs and 350 stolen bases.
Angels general manager Jerry Dipoto told reporters in Cleveland that Trout would play every day -- probably at all three outfield spots -- and that the move was made to "add a little energy, get some spice, shake it up a little bit."
The Angels figure to give Trout a look in the leadoff spot. Their leadoff hitters have batted .195 in the first 20 games with a .250 on-base percentage.
Dipoto flew to Cleveland, arriving at Progressive Field in the fourth inning on Friday, to break the news to Abreu.
Angels owner Arte Moreno will have to swallow the remainder of Abreu's $9 million salary. The team made a similar move last June when it released pitcher Scott Kazmir.
Abreu and Kazmir both were acquired by former general manager Tony Reagins.
Trout reached the majors as a teenager last year and batted .220 with five home runs and 16 RBIs in 40 games. He has long been compared to the Washington Nationals top prospect, Bryce Harper, his teammate in the Arizona Fall League.
Now, they will begin their careers somewhat in tandem. Harper, 19, also was promoted and is scheduled to play in his first major league game Saturday in Los Angeles against the Dodgers.