A monopoly abuse lawsuit against Apple Inc and AT&T over the iPhone can continue as a class action against the two companies, a U.S. judge ruled.

Users of Apple's iPhone have criticized AT&T, the sole carrier for the popular smartphone and the biggest U.S. phone company by revenue, on problems with network quality since the device went on sale in 2007.

An amended complaint filed in June 2008 deals with Apple's practice of locking iPhones with AT&T's wireless network and its control over the applications that can be installed on its smartphone. The lawsuit also consolidates those filed by iPhone buyers starting in late 2007.

District Judge James Ware in the northern district of California on July 8 certified the class suing Apple and AT&T for parts of the lawsuit that deal with violations to antitrust law.

The lawsuit -- which includes any iPhone buyer with a two-year AT&T agreement since June 2007 -- also says Apple secretly made AT&T its exclusive iPhone partner in the U.S. for five years, dampening competition and driving up prices.

Apple and AT&T declined to comment on the judge's decision.

Early in June, AT&T announced plans to stop offering its unlimited pricing plan for new subscribers to its mobile data services, in an effort to improve the speed of its network by cutting down on network-clogging downloads.

The lawsuit seeks an injunction to keep Apple from selling locked iPhones in the U.S. and from determining what iPhone programs people can install. It also seeks damages to cover legal fees and other costs.

The case is In Re Apple & ATTM Antitrust Litigation, U.S. District Court for the Northern District of California No. 07-05152.

(Reporting by Antonita Madonna Devotta in Bangalore, Grant McCool and Ritsuko Ando in New York; Editing by Anshuman Daga, Gerald E. McCormick and Gunna Dickson)