MyxerTones

Myxertones.com is a free service that allows even the simpleminded to make better use of their gadgetry. Simply upload an audio file (mp3 or wav) and Myxertones will send a midi to your phone free of charge. Make sure you check with your service provider about what the messages will cost, but for me (without a text messaging plan), they were only a few cents each.

Elementary instructions, tailored to individual phones, address how to take the audio files from the messages and set them as ringers. I used Audacity to clip some of my favorite tunes down to ringtone length before uploading and came up with some very creative personalized ringtones. Now you can set multiple distinct ringtones and differentiate your callers in the first seconds of the ring.
Myxertones