Even though Apple wasn't at Mobile World Congress this year, the iPhone's presence could definitely be felt.

Mobile applications have been around for years, but it came to the forefront with Apple's App Store, which offered an integrated, easy-to-use way to browse, buy, download, and install applications for the iPhone 3G and iPod Touch. Now that Microsoft and Nokia have announced their own application stores at the trade show, every major player will have a way to deliver mobile programs over the air.

Nokia's virtual storefront opens in May, and it's hoping to outdo its rivals by using location and social networking elements. The service eventually will be open to Nokia's entire fleet of cell phones, and it will be preloaded onto the N97 smartphone.

"It actually suggests things you might like and adds social location dynamics to show you relevant applications, and show you what your friends have bought," said Niklas Savander, Nokia's executive VP of services and software. "And it changes the inventory based on where you are."

Microsoft didn't release many details of its Windows Marketplace for Mobile, but it will likely have a large catalog because there are more than 20,000 programs for Windows Mobile. Microsoft said it would be available in the second half of this year, along with the Windows Mobile 6.5 upgrade and the My Phone content backup service.

It wouldn't be Mobile World Congress without a slate of high-end smartphones, and the manufacturers didn't disappoint. Sony Ericsson showed off the Idou smartphone, which has a 12-megapixel camera, strong multimedia capabilities, Wi-Fi. It's the first handset to officially announce it will use the open source Symbian OS. The handset is in the very early stages of development, though, and it's not expected until 2010. InformationWeek was able to get a hands-on demonstration of the Idou, and the video can be found here.

Samsung introduced a pair of multimedia heavyweights, and the Omnia HD is sure to draw attention when it's released in the second quarter. The Symbian-powered smartphone has a 3.7-inch touch screen, Wi-Fi, 3G, and an 8-megapixel camera that can record videos at 720p resolution.

Nokia had a solid showing with updates to its E Series of smartphones, a handset with an 8-megapixel camera, and a pair of GPS-centric phones. The world's largest cell phone manufacturer also said it would be preloading some handsets with Skype's VoIP software.