Shares of Apple (Nasdaq: AAPL), the world's most valuable technology company, fell  50 cents to $659.50 after the first two hours of Wednesday, in advance of the expected announcement of the iPhone 5 at a product introduction in San Francisco, which isn't scheduled until late morning, Pacific time. Earlier, Apple shares rose as high as $666.90.

Shares of the Cupertino, Calif., electronics company set an all-time high of $683.29 on Monday, before falling back to their current levels.

Over the past year, they've barreled past the $400, $500 and $600 marks. In the first quarter, Apple surpassed Exxon Mobil Corp. (NYSE: XOM) as the world's most valuable company.

Analysts in general have been bullish on Apple, with high estimates for the shares over the next year pegged at $1,111.

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