Carrie Underwood's ex-boyfriend Tony Romo — who now dates Jessica Simpson — still calls her sometimes, but she doesn't always pick up the phone, she tells Allure magazine in the September issue.

"The phone will ring and it'll be him, and I'll maybe not answer," says the singer, 25, of the Dallas Cowboys quarterback, adding that the relationship wasn't serious. "We were both small town people doing very big things, and we relied on each other, dealing with fame."

And true to her hit song "Before He Cheats," Underwood admits she has an unfaithful guy in her past.

"I don't want to name names, even though he probably deserves it, but he fooled around," she tells the magazine. "Oh, yeah, and lied! It was one of those things that everyone knew but me. He was a good liar. Nobody would come out and tell me. And he seemed perfect in every way."

Earlier this year, Underwood says she split from Chace Crawford of "Gossip Girl" via text-messages.

"We didn't have a fight. No one cheated," she tells Allure. "It plain didn't work."

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