Last week, Apple Inc. e-mailed invitations to a media event at its headquarters in Cupertino on Tuesday morning. The invite says ``let's talk iPhone,'' implying the normally secretive company intends to show off the latest version of the device. In the past, Apple has typically introduced a new iPhone during the summer, but this year it was expected to hold off until the fall.

It has been 15 months since Apple began selling the iPhone 4 last June. The first iPhone was revealed in 2007, and the phone's signature slick looks, high-resolution screen and intuitive software made it incredibly popular from the start (the rollout of Apple's iTunes App Store in 2008 helped, too). In addition to gaining millions of fans over the years _ 39 million iPhones were sold just between January and the end of June _ the iPhone and its large App Store have sparked fierce competition from smartphone makers such as those using Google Inc.'s Android software, which was first rolled out in 2008.

Beyond the iPhone itself, the Tuesday event is anticipated as Apple's first major product unveiling in years that won't be led by Steve Jobs, who resigned from the CEO post in August after being out on indefinite medical leave since January. The Apple co-founder is now its executive chairman. And though Jobs did emerge from medical leave twice this year to present Apple's innovations _ most recently in June to show off its new mobile software and iCloud content storage service _ his successor, Tim Cook, is expected to take the lead this time.

Though not nearly as recognizable as Jobs, Cook, formerly Apple's chief operating officer, has been running Apple since January. For years, he has been in charge of Apple's day-to-day operations, and he has long been seen as the natural successor. He also served as Apple's leader for two months in 2004 while Jobs battled cancer and again for five-and-a-half months in 2009 when Jobs received a liver transplant.

Perhaps more important to Apple fans than who is presenting is what the company will reveal on Tuesday. A new iPhone is expected to have a number of changes, the biggest of which will likely be under the hood: the inclusion of Apple's latest iOS mobile software, iOS 5, which has been slated for release this fall.

IOS 5 will include things such as wireless device setup and content syncing, and beefed-up camera, email and Web-browsing apps. A new service called iMessage will allow iOS 5 users to send text messages to each other over Wi-Fi or wireless carriers' data networks, while a folder called Newsstand will corral newspaper and magazine app subscriptions in one place to make it easier to find them. When it comes out, the software will also be available for Apple's iPad, iPhone 4 and 3GS and the two most recent generations of the iPod Touch.

A new iPhone is also expected to include Apple's forthcoming iCloud service, which will store content such as music, documents, apps and photos on Apple's servers and let you access them wirelessly on numerous devices.

As for hardware, a new iPhone isn't expected to look that much different from the iPhone 4, though it could be thinner and have a bigger screen. The existing iPhone is 0.37 inches (0.94 centimeters) thick and has a display measuring 3.5 inches (8.9 centimeters) at the diagonal.

An improved rear camera is anticipated, too. The existing iPhone has a 5-megapixel camera on its rear. A number of recently released smartphones have moved to 8-megapixel cameras.

One of the most notable hardware changes many industry watchers are predicting is the inclusion of a more powerful chip: Apple's dual-core A5 processor, which is the same chip it uses in its current iPad. The iPhone 4 runs on Apple's older A4 chip, and the move to a more capable chip should improve things such as multitasking, opening apps and gaming.

Sterne Agee analyst Shaw Wu said a more powerful chip would be key for getting a feature like voice recognition on the iPhone, which is common on phones running Google Android software. Longtime Apple analyst Tim Bajarin said he wouldn't be surprised to see voice recognition either.

Despite speculation that Apple may show more than one new iPhone on Tuesday, Wu is skeptical. He thinks that in addition to a single new iPhone the company is likely to start selling a version of the existing iPhone 4 with less memory for $99. That would be $100 less than what you'd currently pay to get the cheapest iPhone 4 from one of its two U.S. wireless carriers, AT&T or Verizon Wireless, with a two-year contract.

Analysts also believe Apple could also use the event to trot out new iPods and updates to its iTunes music software, which it usually does in the fall anyway. Last September, Apple announced updates to iTunes and a line of revamped iPods, which included a version of the iPod Nano with a touch screen.

As for when a new iPhone would be available, Wu suspects it would be fairly soon after it is announced. His research indicates production plans Apple set with its suppliers in Asia called for manufacturing to start in October, so he would expect it to be available within a couple weeks of its announcement.

``We would be very surprised if it's longer than that,'' he said.

And as in the past, consumers are likely to clamor for it. Bajarin believes Apple could sell more than 25 million iPhones total during the holiday quarter, which would be well above the 16.2 million it sold during the holidays last year.

``There's huge pent-up demand for this,'' Bajarin said.

Apple shares, which have traded between $277.77 and $422.86 in the past year, fell $6.72, or 1.8 percent, on Monday to close at $374.60.