July 27 (Bloomberg) -- Verizon Wireless filed a lawsuit against rival AT&T Mobility LLC, a unit of AT&T Inc., asking a U.S. judge to rule that it has the “most reliable” mobile phone network.

The suit was filed by Cellco Partnership, which does business as Verizon Wireless, in Manhattan federal court today. It seeks a declaratory judgment that Verizon Wireless’s advertising claims of having “America’s Most Reliable 3G Network” and “America’s Best 3G Network” are “truthful” and “accurate.”

The suit follows a July 1 challenge to Verizon Wireless’s advertising filed by AT&T with the National Advertising Division of the Council for Better Business Bureaus, according to the complaint. AT&T, the largest U.S. phone company, claims Verizon Wireless’s advertising is false.

“AT&T has invented a new formula for calculating ‘reliability’ and claims that by applying this newly concocted formula its 3G wireless network has superior reliability,” the complaint says.

Verizon Wireless surpassed AT&T this year as the largest mobile phone carrier after it acquired Alltel Corp. in January. AT&T is the exclusive U.S. carrier of the iPhone, which helped drive 1.4 million customer additions last quarter. Verizon relied on claims of having the largest and most reliable network to add 1.1 million subscribers in the quarter.

Reliability Measures

AT&T spokesman Mark Siegel had no immediate comment on the lawsuit.

Verizon Communications co-owns Basking Ridge, New Jersey- based Verizon Wireless with Vodafone Group Plc. The company says the appropriate standard for measuring reliability in the wireless telecommunications industry combines two factors: the ability to connect to the network, and the ability to complete a call or download a file once connected. Internal and external studies show Verizon Wireless’s network is most reliable, the suit says.

“AT&T’s claim that speed is an essential component of 3G network reliability and that its formula is the proper standard for measuring 3G network reliability is without any support whatsoever,” Verizon Wireless says.

“Neither the normal and customary usage of the term ‘reliable,’ nor any established industry standard, requires that speed be included in measuring the reliability of a 3G network.”

3G Networks

3G wireless networks incorporate the third generation of standards for wireless communications, as defined by the International Telecommunications Union, which sets standards for telecommunications.

Both carriers are updating their networks, moving toward a fourth-generation technology called long-term evolution, or LTE, to increase Web browsing speeds on mobile phones and laptops. Verizon will get there first, offering LTE in some markets by mid-2010. AT&T is doubling speeds on its current network first and will move to LTE in 2011.

The suit is Cellco v. AT&T Mobility, 09-cv-6656, U.S. District Court, Southern District of New York (Manhattan).

To contact the reporters on this story: David Glovin in Manhattan federal court at dglovin@bloomberg.net; Amy Thomson in New York at athomson6@bloomberg.net.

Last Updated: July 27, 2009 17:08 EDT