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 today — more than a year after it unveiled the iPhone 4.

Last week, Apple Inc. emailed invitations to a media event at its headquarters in Cupertino this 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. 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.

In addition to gaining millions of fans over the years, 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, 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. The Apple co-founder is now its executive chairman. His successor, Tim Cook, is expected to take the lead this time.

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 scheduled 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 them easier to find. 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. 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 such as 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.