Apple does not know when it will have enough iPhone Duos to meet demand, executives said on Monday, the BBC reports. The foldable phone went on sale late last month for $1,999 and quickly sold out, the Verge reports.

"iPhone Duo is constrained as of today," Chief Operating Officer Sabih Khan said on Apple's fiscal fourth-quarter earnings call, according to TechCrunch. "At this time, it's really hard to predict when supply and demand will be in balance."

In an interview with Reuters, Chief Executive John Ternus said Apple is "not able to predict when supply and demand will be in balance," the Verge reports.

Customers who did not preorder or line up at a store are seeing ship times stretch into next year, TechCrunch reports. Verizon has offered gift cards to customers to apologize for the delays, TechCrunch says.

Ternus also said to Reuters that "a very small percentage" of iPhone Duos were returned because of cracked screens, and that Apple is replacing them, the Verge reports.

Apple reported record iPhone revenue of $57.58 billion for its fourth quarter, the Verge reports. The three months to September 26 did not include Duo sales, the BBC says. Mac sales rose 27% to $10.7bn, the BBC reports.

Executives said rising memory costs, driven by demand from the AI industry, are a growing pressure. "What we're seeing with memory pricing right now is unprecedented," Ternus said on the call, according to the Verge. Khan said Apple had raised prices on a number of products "reluctantly," TechCrunch reports.

Khan said supply constraints are expected to continue into next year, particularly for iPads and Macs, the BBC reports.

What we know: Apple says Duo supply is tight and the ramp is going well.
What we don't know: When buyers who order now will get their phones.