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.

The Cingular-iPhone relationship should be troubling for investors, as Pearl has been a significant driver for RIM's stock. The product, widely seen as RIM's attempt to crack the consumer market, was released on Sept. 7 and made available a week later on T-Mobile and through Cingular in November .

RIM shares jumped up more than 80% in response to close at a high of $142.16 on Jan. 8, two days before Apple announced news of its iPhone. Since then the stock has been down about 14%.

Shares of RIM closed down $6.38, or 4.98%, to $121.74 Thursday.

Pearl also played a significant part in pushing revenue for the third quarter of fiscal 2007 to $835.1 million, up 49% from $560.6 million in the same quarter of last year.

State of Dependence

With Pearl, or upcoming phone models aimed at consumers, RIM depends significantly on the carriers to push its devices. RIM's other top customers, including T-Mobile and Toronto-based Rogers ( RG), are less of a risk for the company than Cingular, wrote Ray Sharma, an analyst with GMP Securities, in a research report.

"T-Mobile USA and Rogers are reliable partners who have made a strategic decision to work with RIM," he wrote. "We believe Cingular and Vodafone ( VOD) have plans to diversify away from RIM, which exposes potential financial concerns." GMP Securities does not currently have a banking relationship with RIM or Apple but was a lead underwriter for RIM's initial public offering.

As part of its diversification strategy, Cingular has been promoting the BlackJack and Nokia's ( NOK) e61, wrote Sharma.

What RIM doesn't have to worry about is the Cingular-Apple relationship hurting its business customers. "I don't think the iPhone competes directly with the BlackBerry because it is too glitzy for professional users," says Richard Williams, senior software analyst at ICAP, which does not own shares or have a banking relationship with RIM.

"The iPhone doesn't have features like one-hand operation or a keypad that make the BlackBerry suited for enterprise users," he says.

Meanwhile, RIM is working on other ways to minimize its exposure to Cingular. The company has been working on expanding its partnerships with other carriers -- counting 200 worldwide that now offer BlackBerry -- and has new models lined up for launch in the first half of the year.

RIM is also expanding geographically with business from Asia and Europe becoming more significant. Revenue from the U.S. and Canada contributed 61.1% of overall revenue in the second quarter ended Sept. 2, down from 73% during the same time last year.

Revenue from other world markets grew significantly to 36.9% during the quarter, up from 27% during the same time last year.

The challenge for RIM is to see how it can keep up the heat on Cingular after the iPhone launch while quickly diversifying its customer and revenue base.