Number two US operator AT&T has announced plans to follow its rivals by supporting Google’s Android platform and Palm’s webOS platform. AT&T plans to launch five Android devices during the first half of this year, including exclusive devices from HTC and Motorola. The most high-profile of the five is likely to be its decision to launch an exclusive Android device from Dell, the computer manufacturer that has recently entered the mobile space via operator deals for its Mini 3 device (pictured) with China Mobile and Brazil’s Claro. AT&T’s decision to back Android follows earlier moves by rivals Verizon, Sprint and T-Mobile, and sees the operator offer smartphones that will compete with its own exclusive iPhone offering. It is widely believed that AT&T’s deal with Apple will expire later this year and that AT&T is positioning its new smartphone portfolio to counter any negativity should Apple extend iPhone sales to Verizon Wireless or another US operator. Meanwhile AT&T will also this year offer two Palm devices, but it is not yet known whether they will be new models or the Pre or Pixi. Only Sprint currently offers the Pre and Pixi in the US, although Palm is expected to announce a deal with market leader Verizon Wireless for those two devices this week. “I think this is the best portfolio we’ve ever had if you look at 2010,” enthused AT&T’s mobile chief Ralph de la Vega in an interview with Reuters

AT&T has also made a number of announcements that benefit developers, including reducing the time it takes to review an application before it’s accepted for use by the operator. In addition, AT&T aims to offer all the major application stores on its devices, expanding the market reach for independent developers seeking to bring applications to a broader audience. AT&T already provides access to to Apple’s App Store, Nokia’s Ovi and Microsoft’s Windows Marketplace, but will expand the list to include the Android Market and Palm Catalogue. AT&T will also launch an “Apps for All” initiative, which includes an agreement with Qualcomm to standardise apps development through AT&T’s adoption of the Brew mobile platform. Brew will become the primary operating system for what AT&T calls ‘quick messaging devices’, which make up about one-third of AT&T sales to customers under contract but does not include higher-end smartphones. Those devices have not historically had access to the multitude of apps now available to smartphone users.