SAN FRANCISCO -- Apple Inc. is widely expected to lift the wraps on a new iPhone model next week, updating a product line that has become the largest and most lucrative business for a company historically known for its iconic Mac computers.

But Apple may struggle to maintain the enthusiasm that has whetted investors' appetites and driven its shares to strong gains this year. Previous announcements and an embarrassing and high-profile media leak two months ago may have left the company with little in the way of fresh news to kick off its Worldwide Developers Conference in San Francisco on Monday.

Apple has been known in the past to surprise audiences, though, so company observers do not discount the possibility that there may yet be a surprise or two in store.

Though the week-long event is geared to application developers focusing on all of the company's products, much of the public attention will be on the iPhone, which has become the company's most important product since its heralded launch three years ago.

The event's highlight will be a Monday-morning keynote address by CEO Steve Jobs in which he is expected to introduce the latest updates to the iPhone, as the company has at this same time every year since the device first went on sale in June 2007.

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Apple, of course, has made no official announcement of a new iPhone, though the company was embarrassed by a breach of its famous secrecy in early April, when the gadget blog Gizmodo picked up an apparent iPhone prototype that had been left in a Silicon Valley bar by an Apple employee.

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