Apple’s manufacturing partners are expected to build 2 million iPhone 3GS handsets in the fourth quarter. Thursday of this week marked exactly two and a half years since Apple unveiled the iPhone 3GS during its Worldwide Developer Conference in June 2009. Citing industry sources within Apple’s supply chain, DigiTimes on Friday reported that production of Apple’s iPhone 3GS has continued at high volumes that should hit 2 million units in the December quarter. In the first quarter of 2012, production of the iPhone 3GS will reportedly slow to between 1.4 million and 1.6 million units. The same report also suggests that production of Apple’s CDMA iPhone 4 could top 1 million units in the fourth quarter this year, slowing to between 500,000 and 600,000 units in the first quarter next year. In the United States, Apple’s iPhone 3GS is available for free on contract from AT&T while the CDMA iPhone 4 is sold by both Verizon Wireless and Sprint.