Apple now lets each customer buy no more than two iPhone Duos. Engadget found the cap on Apple's online stores in the US, UK, Japan and Spain when it tried to put a third phone in its cart, and got the same warning in all four.
Try to check out with three and Apple's store stops you: "A maximum of 2 iPhone Duo can be purchased per customer. Please adjust the total quantity of iPhone Duo in your order before checking out." The limit is the same whichever configuration you pick, so a cheaper storage tier doesn't get you a third.
Pre-orders opened on October 16, and shipping estimates slid into January within minutes. That's a long wait for a $1,999 phone, and it's exactly the gap resellers live on. Dozens of iPhone Duos are already listed on eBay, some for more than $5,000, two and a half times what Apple charges.
Apple capped iPhone 5 purchases in the US back in 2012, and it has limited iPhone sales in China several times, at walk-in stores as well as online. It hasn't said why it set this one.
Organised resellers get round limits like this with virtual card numbers, spare email and delivery addresses, or by paying other people to place orders for them, so two per person won't stop them. It does stop one buyer ordering a big batch in a single basket.
If you want one or two, the cap won't touch your order. The wait will. The first phones ship on October 23, and anyone who ordered after the first few minutes is looking at the new year. Some buyers have already seen their delivery estimates move earlier, so a January date isn't fixed.
If you haven't ordered, order now rather than waiting for the dates to settle, and check your estimate again in a few days. If you live near an Apple Store, a walk-in purchase is worth a try once launch day has passed.