At ATL, do not switch frequencies until you are told to do so - regardless of whether its GC to Tower (local) or vice versa. And then know the difference in "contact" and "monitor," we use different instructions at different times in order to minimize frequncy congestion.
This is what everyone should use generally across the board. IAH is the same way. We use "Monitor" all the time...ohh I love when someone calls me when I heard the tower guy go "Monitor ground...." etc.
ATCT