Apple's sales will drop ahead of the iPhone 5's release, which means the company could sell between 15.2 million and 16.2 million iPhones this quarter, Sanford Bernstein analyst Toni Sacconaghi predicts.

Previous Wall Street estimations suggested the iPhone could sell 16.5 million units, Barrons.com reports. Many customers will prefer to wait for the launch of iPhone 5 rather than invest money in a smartphone that is going to be outdated in just three or four months, the analyst explains.

If the iPhone 5 is launched in the first week of September, iPhone sales then decline only 15% Q/Q and reach 20.7 million units; whereas if the smartphone lands in the last three days of the quarter (the worst case), iPhone sales could drop 14% from Q3 to 13.1 million, the analyst suggests.

The iPhone 5 could sell 3 million units in just the first week after launch, since Apple is allowing more carriers to offer its smartphone. In comparison, the iPhone 4 sold 1.7 million in the first week.

The post-launch run-rate is expected to drop by half and continue to drop until it stabilises at a 20% global smartphone share at the end of Q4, Sacconaghi says.

He also advises Apple to attack the Chinese low-end handset market since the high-end market won't grow as much.