Here's what you do, download this program called GoldWave
http://www.goldwave.com/ then take whatever song you want and chop it down to 15-30 seconds long (your ringer only lasts for 30 seconds max) and make it mono. Then you go to
Http://www.sprintusers.com/focus/ and register for an account, after you're done just use the focus tool to send the file to your phone, which can then be downloaded to your phone and used as a ringer
For verizon I'm not sure, I have a razr which you can upload songs via usb.