Spurs general manager R.C. Buford said Jefferson brings youth and health along with his high scoring. Jefferson hasn't missed a game the past two seasons and joins a team that has been the oldest in the NBA for several years.
"His age helps us transition our team into a new era," Buford said.
In a statement, Buford praised the players he gave up.
"Trades are often difficult and saying 'bye' to Bruce, Fabricio and Kurt is a tough thing to do," he said. "All three of them were valuable contributors to our success as well as good people. We thank each of them for their dedication, professionalism and willingness to always put team first."
The move gives the Spurs a dynamic wing scorer to play alongside Tim Duncan, Tony Parker and Manu Ginobili. The Spurs had promised to make their team better this summer and adding Jefferson for role players should give them a huge shot in the arm.
Jefferson averaged 19.6 points and shot a career-high 39.7 percent from 3-point range while starting all 82 games.
Parker said he would welcome a big, athletic player like Jefferson.
"He's a great wing," Parker said. "It's something we don't have on our team."
The Bucks' incentive to make the trade is largely financial. Bowen and Thomas are all in the last year of their contracts. The deal will clear $15 million off the books for the Bucks in 2010-11 and give Milwaukee more flexibility for the 2009-10 season. The Bucks expect to save $4.35 million next season after releasing Bowen (only $2 million guaranteed), a source told ESPN.com.
"The trade we made today provides us with much needed options in both the short and long-term planning for our franchise," Bucks general manager John Hammond said in a statement.
The Pistons will also save some money. Oberto only has $1.8 million guaranteed on his contract. If the Pistons waive him, they'll save $1.7 million this year. That's important to Detroit, which is trying to clear as much cap space as possible for free agents this summer.
The move also opens up some playing time for the Bucks' lottery pick last year, Joe Alexander.
Jefferson became the Bucks' biggest offensive threat after Michael Redd and Andrew Bogut suffered season-ending injuries, but the Bucks' tight financial situation made a move necessary. Milwaukee does not want to pay the NBA's luxury tax, which last year hit teams dollar-for-dollar once they reach $71.15 million in total payroll. These deals will put the Bucks under the threshold.
Redd, Bogut and Jefferson are scheduled to make more than $41 million combined this season.
The trade was a shock to at least one Bucks player: Villanueva posted "RJ traded to Spurs. Wow" on his Twitter account before the trade was official.
Bogut also chimed in, wishing Jefferson the best.
"Sad to see RJ go. He was a fun guy to be around and could play. We are building for the future, slow and steady. Patience grasshopper," Bogut posted on Twitter.
Johnson, a second-round draft pick by Detroit in 2005, started 24 games for the Pistons and averaged 3.5 points and 3.7 rebounds. He is also in the final year of his contract, but makes slightly more than Oberto's $3.5 million, which is partially guaranteed.
Bowen was a key cog in helping the Spurs win three championships, relishing his role as a shutdown defender tasked with guarding the best player on the floor. But the 38-year-old lost a step and saw his minutes cut significantly.
Bowen lost the starting job he held for six seasons and didn't earn a spot on the NBA's all-defensive team for the first time since the 1999-2000 season. Bowen said he still wanted to play but didn't know how many years he had left.
"I'm not looking for any five-year deals," Bowen quipped.
Thomas, 36, is a 14-year veteran who averaged 4.3 points and 5.1 rebounds off the bench last season. Oberto, 34, spent four years in San Antonio and underwent a procedure earlier this month to correct an irregular heartbeat.
Jefferson gives the Spurs the additional scorer they craved in April, when the Dallas Mavericks ousted San Antonio the playoffs in five games. The Spurs were little more than a two-man show of Parker and Duncan, and coach Gregg Popovich said afterward that his team simply couldn't match firepower.
"This provides us an opportunity to have a pretty [darn] good three man on our roster," Buford said.
Chad Ford covers the NBA for ESPN.com. Information from The Associated Press was used in this report.