Verizon has teamed with Google on Tuesday to co-develop several Android-based devices that will be pre-loaded with innovative applications from both parties as well as third-party developers, in an effort to fight off the iPhone and its exclusive agreement with AT&T.

The Google Voice service will be allowed on all Android-powered Verizon handsets, which is likely a direct challenge to Apple and the iPhone. The first two handsets are expected to be released in a matter of weeks.

Analysts expect Verizon Wireless, a joint venture of Verizon Communications and Vodafone  and the largest U.S. wireless service provider, to unveil at least three Android-based phones from such makers as Motorola, Samsung, and HTC later this month.

Backing from Verizon Wireless, which boasts 87.7 million users, could encourage other handset makers to build for Android, too. Device manufacturers may unveil 30 Android-based devices by yearend, says Stifel Nicolaus analyst George Askew. Last summer, Google's top Android manager, Andy Rubin, said he expected up to 20 devices to debut in 2009.

Depending on how aggressively Verizon Wireless begins marketing Android handsets, BlackBerrys and other smartphones could be forced to play second fiddle in Verizon Wireless stores, says Kaufman Bros. analyst Shaw Wu.

You either have an open device, or not, Lowell McAdam, CEO of Verizon Wireless, said in a conference call on Tuesday. And this will be open. We expect to bring that... application to market when we bring the first device out.

Verizon's new open stance is quite a change for the company, which has traditionally kept tight controls over devices on its network. Earlier this year, the nation's largest wireless carrier said it would create its own application store and, at the time, said it would be the only option available for handsets.

The nation's best wireless broadband network is a perfect complement to the innovation of Android-powered services and devices, McAdam said this week. Together, we'll work to deliver a compelling new experience to our customers.

For Google, the deal with further expand the Android platform which, for a majority of its first year on the market, was only available on one device and on one carrier in the U.S.

The Android platform allows Verizon Wireless customers to experience faster and easier access to the web from any location, said Eric Schmidt, chairman and CEO of Google. Through this partnership, we hope to deliver greater innovation in the mobile space to consumers across the U.S.

Apple has refused to accept the first-party Google Voice application onto the iPhone App Store, stating that the software too closely mimics its own default phone software. However, both Google and Apple disagree on whether the application was formally rejected from the App Store.