LINDSAY LOHAN was on "Letterman" last night . . . and during her interview, she and Dave prank called OPRAH WINFREY. It wasn't much of a "prank call," but Dave did pretend to be Lindsay's secretary at first.
It's unclear how much of it was planned, but Oprah DID seem surprised. When Dave asked Oprah how Lindsay was doing, she didn't have a ringing endorsement. She said, quote, "I think she's doing really OK . . .
"Uh, you know, to have cameras following you around through every phase of your life, and you're trying to pull your life together, I think that's a really difficult thing . . . she's making some progress." (Here's video.)