4:09pm: Two sources tell Mark Murphy of the Boston Herald that the Mavs and Celtics haven't engaged in any trade talk about Rondo, with one of the sources calling the notion "ridiculous."
2:11pm: The Celtics want Dirk Nowitzki in return for Rondo, and that's gummed up trade talks between the teams, reports Marc Stein of ESPN.com (Twitter links). The Celtics are interested in Mavs draft acquisition Shane Larkin, too, notes Adrian Wojnarowski of Yahoo! Sports (Twitter link).
2:05pm: The Mavericks are interested in acquiring Rajon Rondo from the Celtics, a source confirms to Gary Washburn of the Boston Globe. Mike Fisher of DallasBasketball.com originally reported the Mavs' engagement in talks with Boston. The Mavs would love to acquire Rondo as part of a recruiting effort to land Dwight Howard, tweets Adrian Wojnarowski of Yahoo Sports, but Wojnarowski cautions that the Celtics would require the Mavs to absorb multiple contracts as part of a trade. Taking back salary along with Rondo could make it difficult, if not impossible, for the Mavs to sign Howard.
Rondo has $24,863,636 left over the final two seasons of a team-friendly contract that ends in 2015. Celtics president of basketball operations Danny Ainge told reporters Thursday that his team will not trade Rondo, but that won't stop the Mavs from asking, Washburn writes. Once the 2013/14 season officially starts in July, Dallas will have the cap space necessary to absorb Rondo's contract without taking on any other players. Still, Washburn figures the Mavs will want to send Shawn Marion's contract to the C's along with a younger player and a draft pick to entice Ainge into making a deal. Given Wojnarowski's report, I'm not so sure the Celtics would want Marion, but that's just my speculation.
The Mavs figure to have about $36MM in guaranteed salaries for next season, leaving just about enough room to sign Howard. Taking on Rondo without giving up an equal amount of salary in return wouldn't leave enough space for Howard or any other maximum-salary free agent, so I don't think a Rondo-Howard collaboration is likely in Dallas, unless the Mavs can engineer a series of other moves.