Apple is unable to meet demand for the iPhone Duo and there’s no timeline for when the company will catch up, CEO John Ternus told Reuters following today’s earnings report . Duo is constrained as of today. The ramp is going well, and we’re working hard to get it to as many customers as quickly as possible, but at this point, we’re not able to predict when supply and demand will be in balance. Ternus commented on the display issues some customers have seen, saying that "a very small percentage" of units have been returned and Apple is offering replacements…