The iPhone is such a highly visible product, and Apple’s sales projections so important, that Toni Sacconaghi of Bernstein Research believes that it could become crucial to the future of the company, for good or bad, according to MarketWatch on Friday.

One driver, according to Mr. Sacconaghi, is the major contribution of the iPhone to Apple’s sales growth, accounting for a fourth of total sales within four years. Secondly, the high gross profit margin of the iPhone, 55-60 percent, compared to the rest of Apple’s products, 30-33 percent, could be responsible for about 80 percent of Apple’s earnings growth.

On the other hand, there are some emerging issues that could be a source of concern. "While we believe the iPhone has the potential to drive material earnings growth for Apple, recent data points suggest the business is facing two significant challenges: (1) overall demand for the handset appears to be falling short of expectations; and (2) the incidence of ’unlocking’ has been much higher than expected," Mr. Sacconaghi wrote in a recent report.

The unlocking issue isn’t related to sales, rather, it’s related to the loss of additional shared revenue when an iPhone is sold through an authorized partner. It can be compared to the movie industry where movie sales could be booming, but investors feverishly focus on the lost sales opportunities caused by pirating.

"On balance, we believe Apple is now reasonably to attractively valued, especially in light of the company’s strong free cash flow generation," wrote Mr. Sacconaghi. "However, we remain worried that the near-term news flow on iPod and iPhone could be incrementally negative." He gave AAPL a neutral rating.

The recent tumble of Apple’s share price has been driven by many factors: disaffection with hightech stocks and worries about the U.S. economy. Even so, Apple has some challenges to face to restore investor confidence that the company can navigate through the sticky issues of unlocked phones, pricing, solid sales projections, and a seamless introduction of next generation phones.

Because lost revenue due to iPhone unlocking is such a strategic issue, Mr. Sacconaghi believes that Apple will either have to worker harder to keep the iPhone locked, or, alternatively, accept the situation and sell an unlocked version -- one in which associated carrier revenue is not expected.