By Sam Oliver

Published: 08:00 AM EST (05:00 AM PST)

(Mobile World Congress) Apple is not officially present at this week's Mobile World Conference in Barcelona, Spain, yet carriers are talking about the iPhone and rivals are introducing what they hope to pitch as "iPhone killers."

On Monday, Microsoft is widely expected to unveil Windows Mobile 7, its latest mobile operating system that looks to compete with the iPhone. Others have already introduced new phones or products that aim to compete with the iPhone and its App Store.

Apple is the second-largest smartphone maker in the U.S., with 25 percent of the market, and the third-largest in the world. The handset is present at this week's Mobile World Congress, with the iPhone 3GS as part of the official display for German carrier Deutsche Telekom, owner of wireless carrier T-Mobile in the U.S.

A T-Mobile spokesman told The New York Times that T-Mobile U.S. would "definitely be interested" in the iPhone if Apple were to ever offer it on multiple carriers. The handset is currently exclusive to AT&T.

The Times noted Apple's unofficial presence and importance at this week's trade show, despite the fact that the Cupertino, Calif., company is not an exhibitor. A spokeswoman for the GSM Association, the organizer of the annual event, said Apple would be welcomed if they decided to exhibit at a future event.

"Secretive and focused, Apple rarely ventures beyond its own well-staged promotions," the report said. "The company has sent executives to the Barcelona show, but has never taken center stage."

AT&T, Sony, LG partner for own app store

Hoping to take on Apple's wildly successful App Store, the GSM Association announced Monday that 24 telecom operators have formed an alliance to build an open platform for applications. Support for the venture has come from LG Electronics, Samsung and Sony Ericsson, according to Reuters.

Other partners listed include AT&T, China Mobile, Orange, Telefonica and Vodafone. Combined the wireless providers listed are responsible for more than three billion customers worldwide.

The alliance reportedly seeks "to unite members' developer communities and create a single, harmonized point of entry to make it easy for developers to join."

With more than three billion downloads to date, Apple's blockbuster App Store has been a major selling point for the company's iPhone. At last months' iPad unveiling, the company revealed that there are more than 140,000 applications available on the App Store.

'Life changing' Samsung Wave takes aim at iPhone

The first handset running the Samsung Bada platform, the Samsung Wave, was introduce before the Mobile World Congress Monday. Featuring a 3.3-inch anti-smudge AMOLED screen, 1GHz processor, 5 megapixel camera, and 720p video playback, the handset is expected to arrive in April.

First introduced last fall, Samsung Bada is built on top of Linux and sports an open SDK. Unlike Symbian or Google Android, the platform is exclusive to Samsung phones.

According to The Daily Telegraph, Bada will ship with an iTunes-style app store that will offer games, maps, e-books and other applications.

The Samsung Wave was introduced Monday as an iPhone rival. Photo courtesy Reuters

No price was announced, but the Samsung Wave is expected to undercut Apple's iPhone 3GS, which starts at $199. The Wave will be backed by a £6 million advertising campaign from Samsung.

"We're delighted and extremely excited about the launch of Samsung Wave -- the first handset to run on the Samsung Bada platform and the first to feature a stunning Super AMOLED screen," said Mark Mitchinson, vice president Samsung Mobile UK said. He added that the handset's Social Hub "offers a life changing user experience."