Apple Inc unveiled a cheaper notebook with revamped software on Monday, kicking off a closely watched annual conference with low-key announcements amid speculation visionary leader Steve Jobs might appear after a months-long absence from public view.

Shares in Apple slid 2.9 percent to $140.48 -- after a 6.5 percent climb in the week leading up to the much-anticipated event. The stock briefly headed even lower after CNBC reported that Apple planned to price new iPhones aggressively, and refresh its entire line of the popular smartphones.

Among other incremental announcements, the consumer electronics giant showed off a new 15-inch notebook with improved battery life, a $300-cheaper Mac Air -- its thinnest laptop -- and, as expected, its highly previewed Snow Leopard Mac operating system software.

Apple's new MacBook Air notebook now starts at $1,499. The company also unveiled a new 13-inch MacBook Pro starting at $1,199, and a 15-inch laptop with longer battery life, addressing a perennial consumer concern.

Apple's stock is historically volatile during the company's June developer conference. It dropped about 7 percent over the course of the conference in 2008 and about 4 percent in 2007.

Chief Executive and founder Jobs had not appeared halfway through the event.

Suspense and speculation had mounted in the months before Apple's annual Worldwide Developers' Conference, with hopes ranging from a cameo by Jobs -- out till the end of June on medical leave -- to revelations of a game-changing tablet mini-PC or cheaper iPhone.

Jobs, a pancreatic cancer survivor, has not appeared despite speculation he would, after springing his leave of absence on stunned markets in January by saying his health problems were more complex than previously thought.

Despite a slowing product line, worsening consumer spending and an uncertain succession plan, investors have quickly got comfortable with the idea of a Job-less Apple. Shares in the maker of the iPod and iPhone have surged 85 percent since shortly after the bombshell was dropped on January 14.

Jobs, a college dropout, co-founded Apple in 1976 with his friend Steve Wozniak in a Silicon Valley garage. After a falling-out with the board, he left the company in 1985.

Apple floundered, setting the scene for his return in 1997. The company has flourished under Jobs 2.0, rolling out the concept of a computer as a 'digital hub' along with the now-ubiquitous iPod and iPhone.

(Additional reporting by Clare Baldwin; Writing by Edwin Chan; Editing by Peter Henderson and Richard Chang)