The salesperson, a calm woman named Sarah, nodded. "Great deal. You just need to add a second line and stay on the Unlimited Platinum plan for 36 months."

Leo realized he’d stumbled into the best BOGO deal of all:

Leo sprinted to the mall. "I’m here for the BOGO," he panted, sliding his current phone—which had a screen like a spiderweb—across the counter.

Leo lived by a simple, if somewhat exhausting, rule: . He was the king of coupon clipping, the master of cash-back apps, and a professional waiter of "seasonal clearances." But his ultimate white whale was the "Buy One, Get One" (BOGO) iPhone deal.