Apple (NASDAQ:AAPL) has started training its retail store employees in the U.S. for an iPhone trade-in program ahead of the highly expected unveiling of the new iPhone 5S and the iPhone 5C on Sept. 10, according to a new report.

The Cupertino, Calif.-based tech giant has sent training material to company retail stores in the country to familiarize employees with the iPhone trade-in program, MacRumors reported, adding that the first line of store employees were expected to receive the related instructions on Monday, while other employees would be trained next week, ahead of the launch of the program.

The report stated that Apple might announce the new iPhone trade-in program alongside the unveiling of the next generation iPhone models -- the iPhone 5S and the iPhone 5C -- at a special media event on Sept. 10.

A report from 9to5Mac, on the other hand, said that the roll-out date for the trade-in program was not yet clear, but it was almost confirmed to take place during the month of September. The report also said that Apple wanted the training to be completed by Sept. 7.

TechCrunch also noted Apple’s plans about an iPhone trade-in program, and said it was already live at a number of Apple stores in the U.S. Here is how the report explained the execution of the program:

‘A customer brings a working, non-liquid-damaged iPhone into an Apple Retail Store. It’s then evaluated by an employee with the help of an online site that an employee can access using the store’s iMacs or iPads. The customer then answers a series of questions about the condition of the device in order to determine a value.

That value can be used in credit for a new device but only if the customer has an upgrade credit available. So there is a carrier check involved. If a user does not have an upgrade credit, they could presumably pay the early termination fee of their carrier and use the credit towards a new device on another carrier.’

Although the value of an older iPhone model can depend on many factors such as color, physical damage and liquid damage, TechCrunch said that the exchange value of a 16GB iPhone 4 or 4S could be around $120-$200, while a 16GB iPhone 5 in good condition could go for around $250.

Rumors about Apple gearing up to launch an iPhone trade-in program first appeared in June when Bloomberg reported that the company could soon launch such a program in partnership with recycling firm Brightstar, to encourage users to upgrade to the existing iPhone 5 and turn in older models.

The iPhone trade-in program is considered to be a significant part of CEO Tim Cook’s plan to bolster iPhone sales at company retail stores, which according to him, sell only one out of five iPhones sold in the U.S.

“I see channels doing it, and I like the environmental aspect of it, and so that part of it really is encouraging to me,” Cook said, during Apple’s June quarterly earnings call, according to reports. “The reason that is so attractive around an iPhone is that the residual value of an iPhone stays so high. That makes the trade-in programs a win-win from many points of view.”

Apple’s iPhone 5S, featuring a new A7 processor, is expected be much faster than the iPhone 5. The new flagship smartphone is rumored to include an improved camera and a fingerprint sensor within the home button. The phone is also expected to be available in a golden or champagne color.

The so-called low cost iPhone 5C is said to be similar to the iPhone 5, but might be repackaged into a plastic shell and be available in multiple colors.