Buckner, 24, was a second-round pick in the 2004 First-Year Player Draft and made his Major League debut last season. He went 1-2 with a 5.29 ERA for Kansas City in 2007, a season in which he started at Double-A Wichita before being promoted to Triple-A Omaha.
While with Omaha, Buckner was 9-7 with a 3.78 ERA and was named the team's Pitcher of the Year. In 96 Minor League games, he is 32-29 with a 4.31 ERA and has compiled 433 strikeouts in 478 1/3 innings.
Callaspo was acquired by the D-backs prior to the 2006 season from the Angels. He was outstanding that year for Triple-A Tucson, where he hit .337 and compiled an .882 OPS. His Minor League success didn't translate to the big leagues in 2007, when he hit .215 in 56 games and was involved in a much-publicized domestic disturbance incident with his wife.
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.