There is no app needed. Just ssh into the phone, find the UI sounds directory, and change the name of your sms tone to.... SMS-received-1, or 2, or 3, ect...What I would do though is rename the original to .bak or something, that way if you ever wanted to revert back to it you could. I hope this helps!
EDIT: Also make sure the sound file is a .caf file...