The righty dominated Double-A hitters in 2006, working to a 15-8 record and 2.67 ERA in 28 starts. He walked just 34 and fanned 153.
He was the Rays' 13th-round pick during the 2004 First-Year Player Draft.
"Sonny has put up good numbers throughout his Minor League career, and he's doing it again this season in Triple-A," Rays manager Joe Maddon said. "He's not what you'd consider a 'stuff' guy, but I don't think he could walk away from success.
"Sometimes, you just try to scout and evaluate high-velocity when it comes to pitchers, but I do believe in pitchers that can pitch, and I do believe he is one of those guys."
Howell, who'll get the ball on Sunday against the Royals, has worked to a 3-5 record and 3.96 ERA through 11 starts with the Bulls, which includes one complete game. The southpaw has spent parts of two seasons in the Majors, including last year in Tampa Bay. He made eight starts for the Rays after he arrived from Kansas City via a midseason trade, and went 1-3 with a 5.10 ERA. Howell is 4-8, 5.79 through 23 career games.
"With J.P., you're really working with the command of the pitch, his overall makeup and his tenacity out there," Maddon said. "He's been pitching well."
Tampa Bay pitchers Jae Seo (designated for assignment) and Jae Kuk Ryu (opetioned to Durham) were shifted in order to clear room on the roster.
Seo struggled mightily with his composure during many of his 10 starts, and averaged nearly two baserunners per inning. The right-hander was bumped from the rotation to the bullpen Sunday after he posted an 8.10 ERA. Seo was tied with Fossum for most homers allowed (11).
Ryu came to Tampa Bay in a February trade with the Cubs in exchange for two Minor Leaguers. The Rays hoped he'd add competition to the starting rotation, but instead he went 1-1 with a 5.06 ERA in 15 relief appearances this season.
Maddon said Ryu would start for the Bulls.
The Rays also took pitcher Jon Switzer off of the 60-day DL and optioned him to Durham.