Warren Buffett.APThe Department of Justice is suing Apple for monopolizing smartphone markets with the iPhone.Regulators called Apple's defenses against its rivals a "moat," borrowing Warren Buffett's metaphor.Buffett's Berkshire Hathaway is one of Apple's biggest shareholders with a nearly 6% stake.The Department of Justice is suing Apple for monopolizing smartphone markets — and cheekily used a term coined by Warren Buffett to make its case against the investor's No.