There is no way Memphis gives up Gay, Conley and the number 2 for Rondo. Maybe 2 of the 3 (maybe), but no way they give up all three.
I don't know why Memphis is viewed as a good destination for Rondo. Memphis is putting their future in OJ Mayo's hands - he'll be dominating the ball at all times. They don't need a point guard who handles all the time, just one who can hit open shots, play defense and pass (generally to Mayo). I don't think there's anything to this particular rumor.