I went from an HTC Touch to my BB Curve 8330. I love my BB but I am missing the MP3 Trimmer app from my HTC. It would allow you to trim out a particular portion of an mp3 and save it as a seperate file name. From there you could send it mms or assign it as a ringtone.
i don't know of any BB apps that can do this (but i'm fairly new to checking out BB apps) but i do know you can use a program called goldwave for windows.
sorry i couldn't be of more help