LOS ANGELES  AT&T, one of the biggest corporate sponsors of “American Idol,” might have influenced the outcome of this year’s competition by providing phones for free text-messaging services and lessons in casting blocks of votes at parties organized by fans of Kris Allen, the Arkansas singer who was the winner of the show last week.

Representatives of AT&T, whose mobile phone network is the only one that can be used to cast “American Idol” votes via text message, provided the free text-messaging services at two parties in Arkansas after the final performance episode of “American Idol” last week, according to the company and people at the events.

There appear to have been no similar efforts to provide free texting services to supporters of Adam Lambert, who finished as the runner-up to Mr. Allen.

Since then, angry supporters of Mr. Lambert have flooded online chat boards with messages claiming irregularities in the competition’s voting.