To add ringtones (or notifications or alarms) to Android phones, connect the phone to your computer and go to the top level of the drive that is mounted. Under that drive you can create (though they may exist already):
/alarms or /media/alarms or /media/audio/alarms
/notifications or /media/notifications or /media/audio/notifications
/ringtones or /media/ringtones or /media/audio/ringtones
In theory putting it under “/media/audio” (the third version given) should be a little cleaner. It also sounds like you can put it just about anywhere and tap on the track to select “Use as phone Ringtone” (I have not tried this though).
This is under Android OS 2.1. Your mileage may vary with other versions.
The Android API documentation is here, however it doesn’t look all that useful for the average end user.
UPDATE:
Well, that’s interesting. Having just tried my instructions again, I found I had to create a:
/media/ringtones
and put them there. “/media/audio” didn’t seem to work.
Something must have changed in the latest version…
/sdcard/notifications OR /sdcard/media/notifications
/sdcard/ringtones OR /sdcard/media/ringtones