It's officially an open secret now: T-Mobile is going to announce CallerTunes, aka their version of ringback tones,
tomorrow. No word on pricing or selection yet, but we'll have details for you soon.
P.S. - In case you aren't familiar with ringback tones (and believe us, you will be very sick of them soon), they're basically customized audio clips that callers hear when they dial your number instead of the usual ringing sound. The carriers like 'em because they're one more thing they can charge people for.
[Thanks, anonymous tipster]