Tim Cook kicks off Apple's iPhone event

CUPERTINO, California (Reuters) - APPLE (AAPL.NQ)Inc CEO Tim Cook walked onstage to kick off a Tuesday event at which the company is expected to introduce the fifth version its iPhone.

Cook, an operations and supply-chain expert not known for pitching products, will preside over the new smartphone's launch at Apple's headquarters in Silicon Valley, standing in for co-founder Steve Jobs in his new role as chief executive.

Jobs, a pancreatic cancer survivor who stepped down as CEO in August after taking his third medical leave, has not yet appeared on stage.

Some shareholders and analysts expect a cameo appearance by Jobs, now chairman, though a no-show would not be a major disappointment.

Apple launches are some of the hottest events on the tech calendar. Tuesday's "Let's talk iPhone" show marked Cook's unofficial debut since taking over from Jobs in August.

The new iPhone, expected to be faster, thinner and larger-screened, is likely to come loaded with the updated iOS5 software that Apple unveiled in June. Some of the new features include improved notification functions and better Twitter integration.

The iPhone, which accounts for over 40 percent of Apple's sales, has been a big success since it came out in 2007, making Apple into one of the world's leading consumer electronics companies.

But Apple would be launching the latest version at a time when the economy is slowing and competition is intensifying. More than 550,000 Google Inc Android-based devices -- including tablets -- are activated each day.

The new iPhone faces competition from phones based on the Android operating system, such as Samsung Electronics' Galaxy line.

(Writing by Edwin Chan. Editing by Phil Berlowitz and Robert MacMillan)