With the iPhone, said Sanford C. Bernstein & Co. analyst Toni Sacconaghi, "They have captured the hearts and minds of consumers."
Apple gets about 70 percent of its profit from the iPhone, Sacconaghi said. The company's stock has risen an average of 11 percent in the two months before previous iPhone updates have been released, he said.
The new iPhone will have a larger screen and thinner body, and is expected to work with faster, long-term evolution wireless networks being introduced by carriers such as Verizon Wireless and AT&T Inc., according to analysts including Piper Jaffray Cos.' Gene Munster.
In addition to the iPhone, Apple also plans to introduce a smaller, cheaper iPad by the end of this year, people familiar with the plans said in July.
Apple, already the world's most valuable company, has surged more than sevenfold since the iPhone debuted in January 2007. The stock has climbed 64 percent this year.
Because Microsoft's record was set during the Internet boom when valuations were inflated by predictions that later failed to materialize, a more significant long-term milestone would be if Apple's market value tops $1 trillion, David Yoffie, a Harvard Business School professor who has written about Apple, said in an interview.
"We're in a period now of much more normalcy, which makes Apple's accomplishments even more impressive," Yoffie said.
While the popularity of the iPhone and iPad make it possible that Apple might surpass that $1 trillion mark, it can be difficult for technology companies to maintain a run of the kinds of successes that Apple has had over the last decade, he said.
"It doesn't take much to miss a cycle," Yoffie said. If the anticipated iPhone 5 and smaller iPad are very good or great "then the valuation will be easily justified. If, for any reason, they have a hiccup on any of these products, then Apple would be vulnerable."
PetroChina Co. became the world's first company to be valued at $1 trillion, when the shares almost tripled on its first day of trading in Shanghai in 2007.