Billionaire Carl Icahn invested in Apple yet again, saying the company is “extremely cheap” as its stock continues to fall.Icahn, who up until two days ago was actively pursuing a take over of Dell, has been touting Apple as undervalued. Last month, he purchased a “large position” in Apple, tweeting about his conversations with the company’s chief executive Tim Cook. At the time, he alluded that the conversations were not over and that he and Cook would talk “again shortly.” Seems those communication lines did, in fact, stay open, as Icahn told CNBC that he’d bought “quite a bit” of Apple’s stock.He did not tweet about today’s purchase, but he did further express to CNBC that, for him, Apple is a “no brainer.”The company released its latest set of iPhones, set to be officially released to customers on September 20. Instead of lowering the price on its iPhone 5, Apple decided to come out with two new versions of the 5: the 5C and the 5S. The 5C is a slightly pared down version that comes in a range of colors due to its plastic body. The 5S offers all the new hardware upgrades, and is made out of metal.The announcement didn’t do much for Apple’s stock, however. It tumbled $29 a share today and continued to drop five percent in after-hours trading. Unfortunately, Icahn’s influence hasn’t affected Apple’s share price today, which closed at 467.71.When Icahn announced his first investment in August, the company’s stock jumped to $500 for the first time since January.