What did Steve Jobs do to his old buddy Bono? The Irish rock star, once the Apple CEO's adoring buddy, is funding the most credible threat to the iPhone yet.

Bono is a founder of Elevation Partners, the Silicon Valley private-equity firm named after the U2 song. And Elevation just sank another $100 million into Palm, the troubled smartphone maker. Palm, which waited too long to switch its product lineup from electronic organizers to souped-up cell phones and whose Treo smartphone is showing its age, lost more than $500 million in the most recent quarter. Bono's firm now owns 39 percent of Palm.

He's also lassoed several former Apple executives into the Palm corral. Fred Anderson, a former Apple CFO and board member, is an investor at Elevation. Jon Rubinstein, a hardware executive who served as Jobs's right-hand man at Apple, resigned in 2006 — one day before the company's 30-year anniversary — and joined Palm a year ago. Rubinstein, the company's executive chairman, is working on a new family of devices that will compete with Apple's iPhone; the big unveiling is planned for the CES computer trade show next month.

The last CES was also the scene of the latest dig by Bono at Jobs. In January 2008, he appeared in a farewell video for Microsoft chairman Bill Gates. Later that month, he shilled for Michael Dell, the founder of the eponymous PC maker who once called for Jobs to shut down Apple and "return the money to shareholders." (Apple is now worth far more than Dell. Ha!)

And to think they were once so close. At an Apple event in 2003, Bono called Jobs "the Dalai Lamai of integration." One year later, Bono and Jobs introduced a U2-branded edition of the iPod. Jobs, who is rarely seen in public, attended a U2 concert in 2005, and Bono praised Apple as being "more creative than a lot of rock bands." In 2006, Bono promoted a red iPod for his Product (Red) charity scheme.

So what happened? The falling out has never been publicly explained, but I have a theory on what happened.

Apple's board of directors fingered Fred Anderson, the former Apple CFO, in a probe over stock-options backdating at Apple. In a public statement, Anderson blamed Jobs. Things got messy, and Anderson resigned from the board after reaching a settlement with the SEC.

At that point, Anderson was already at Elevation helping make Bono, whose net worth is estimated in the hundreds of millions of dollars, even richer. So Jobs wasn't just messing with Bono's pal; he was messing with his pocketbook.

It hardly squares with the Irish rocker's saintly save-the-children image, does it?