LOS ANGELES - Fox Broadcasting and the companies that produce “American Idol” said Wednesday that they were “absolutely certain” that the outcome of voting for the winner was not unfairly influenced by free text-messaging services offered to fans of Kris Allen, the winner, at viewing parties in Arkansas last week.

AT&T, meanwhile, said it would advise its employees not to offer services that favor one contestant over another on “American Idol” or similar shows.

The statements followed reports that AT&T representatives offered free texting services and instructions in sending multiple, simultaneous text messages at viewing parties in Mr. Allen’s home state.

When contacted Tuesday, Fox had declined to comment. The voting rules for “American Idol” forbid “power voting” using “technical enhancements.” Representatives of Fox and AT&T declined to comment on whether similar texting services were offered at other viewing parties this year or in previous seasons.

A Fox spokeswoman declined to comment on the margin of victory that Mr. Allen held over the runner-up, Adam Lambert. But the Fox statement dismissed the possibility that the Arkansas parties had influenced the outcome of this year’s finale.