Apple sold 5 million iPhone 5s during the first three days it was on sale, which is way below analyst expectations, who were calling for 6-10 million in opening weekend sales.

So what went wrong? Analysts are blaming the iPhone 5 pre-orders.

Piper Jaffray analyst Gene Munster: "Our sales expectation assumed that Apple would include all phones pre-ordered online. We believe that this may have been up to 1 million additional units as units pre-ordered after the middle of the first day were projected to be available in October."

Topeka Capital's Brian White: "We believe this shortfall is largely due to supply availability and the fact that most consumers are opting for the pre-order option."

ISI Group's Brian Marshall: "The 5mil+ iPhone 5 reported sales only takes into consideration: 1) what was sold into partners (e.g., retail outlets, carriers, etc.), 2) sold in AAPL retail stores, and 3) direct to customers only if they signed for the device. Importantly, this doesn't take into consideration units in delivery direct to customers (i.e., AAPL must have signature of acceptance by customer before it is counted as a sale) and we estimate units in transit could be in the millions currently."

Apple announced 2 million iPhone 5 pre-orders. Analysts started baking those into their opening weekend sales. But, only a portion of the pre-orders were shipped to customers on Friday. So, it's unclear how many pre-orders were included in the opening weekend sales.

Further, over the phone Brian White told us he thinks customers are getting more and more comfortable pre-ordering the phone. They see that it's easy to get the phone and set it up on their own. They don't have to wait in a line and they don't need customer service.

As a result, more and more people are pre-ordering, thus denting the opening weekend sales growth.

White said the initial demand, as demonstrated by pre-order sales, shows interest in the iPhone 5 was very strong and growing.

However, on Twitter, BTIG analyst Walter Piecyk notes that Apple said, "the majority of pre-orders will be delivered to customers on 9/21," when it announced iPhone 5 pre-orders. If the majority of pre-orders were shipped, then it sort of kills the analyst theory around pre-orders.

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