SAN FRANCISCO • Apple fans are amped. The computer and gadget maker is expected to announce a new, more powerful version of its wildly popular smartphone this week — more than a year after it unveiled the iPhone 4.

Last week, Apple Inc. emailed invitations to a media event to be held this morning at its headquarters in Cupertino, Calif. The invite says "let's talk iPhone," implying the normally secretive company intends to show off the latest version of the device.

It has been 15 months since Apple began selling the iPhone 4. 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. Beyond the iPhone itself, today's 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.

Perhaps more important to Apple fans than who is presenting is what the company will reveal today. 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 synching 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 on Apple's servers and let you access them wirelessly on numerous devices.