Neither the nifty features of Apple's ( AAPL) iPhone nor the hype around the launch should really concern rival smartphone maker Research In Motion ( RIMM). RIM's Achilles' heel is likely to be its partnership with Cingular and its dependence on the wireless carrier for a significant portion of its revenue. RIM's top two customers provided 19% and 17% of the company's fiscal 2007 second-quarter sales. Though RIM has never disclosed the names of these customers, they are widely believed to be T-Mobile owner Deutsche Telekom ( DT) and Cingular, respectively. Consider now that Cingular is the sole carrier for iPhone, and RIM has something to worry about. Cingular's exclusive relationship with Apple could give Cingular less of an incentive to push RIM's phones. Even before the iPhone, there have been questions about Cingular's commitment to RIM. Cingular has been heavily promoting Samsung's BlackJack phone . "We are already beginning to see encroachment on RIM's strong position from BlackJack, and it is interesting that Cingular has not put out any joint ads with RIM in recent weeks," says Kenneth Leon, senior equity analyst at Standard & Poor's, which does not have a banking relationship or own shares of RIM or Apple. Any financial impact of lost business from Cingular is unlikely to affect RIM until the second half of 2007 because the iPhone doesn't launch till June, says Leon.