I'm pretty sure ring backs are a carrier specific option. Not something you can just add to your phone.
That's what I am thinking. But how can they keep charging you for the same ringback every 6 months? %$#*%# It would cost you a fortune to have several. So I only have one (that one came free for the first 6 mo) and people must be tired of hearing it.

They probably can't get the Black Eyed Peas out of their heads. "I gotta feeling....that tonight's gonna be a good good night." Darn, now I can't get it out of my head.