Apple is beginning final preparations to launch an iPhone trade-in program in its retail stores as soon as next month, according to sources with knowledge of the initiative. This trade-in program will allow customers that own earlier versions of the iPhone, such as the iPhone 4S, to bring the phone into an Apple Store and exchange it for a new iPhone model, like the iPhone 5, at a discounted price. On the allure of a trade-in program, Apple CEO Tim Cook said during the last earnings call that he is “not opposed” to such a strategy. “I see channels doing it, and I like the environmental aspect of it, and so that part of it really is encouraging to me,” said. Third-party iPhone sales channels like Best Buy, Verizon Wireless, and AT&T have been pushing their own trade-in programs for several months.