Apple has increased the total order volume for iPhones for the second half of 2011 by nearly 13 percent. It is believed that 26 million of those will be iPhone 5 units, according to DigiTimes, citing Taiwan-based supply chain makers.

The total number of iPhone 5s planned to ship in the second half of this year is impressive, but it’s the quarterly breakdown of orders that’s most interesting.

“Phone 5 orders for the third quarter of 2011 have been lowered from seven million units to 5.5-6 million units, while fourth-quarter orders have been raised from 14 million units to more than 20 million units,” said DigiTimes. “Total orders for iPhone 3GS, iPhone 4 and iPhone 4 CDMA for the third quarter exceed 20 million units, and fourth-quarter orders have been reduced to eight million units, the sources indicated.”

Shipping 26 million new iPhones is right in line with what we heard last month from the Wall Street Journal regarding Apple’s sales estimates for 2011.

"Apple's sales estimates of the new iPhone are quite aggressive," a person at one of Apple's suppliers told The Wall Street Journal. "It told us to prepare to help the company meet its goal of 25 million units by the end of the year."

If Apple is lowering orders for the iPhone 5 in the third quarter and increasing production in the fourth quarter, this strengthens rumors that the company’s next phone is going to be launched in October rather than September.

Pushing back production could also mean that Apple did experience some issues with the A5 chip overheating as previously thought.

The GSM iPhone 4 was released on June 24, 2010 and sold 1.7 million units in three days. Steve Jobs called it the most successful product launch in Apple's history. By comparison, the company sold 1 million 3GS' in the same timeframe. The CDMA version launched on February 10, 2011 and surpassed Verizon’s all-time record for sales of a single device.

Apple is expected to ship 95 million iPhones in 2011, consisting of iPhone 3GS, iPhone 4 and iPhone 5 models.