This is the most less expensive program of its kind!
It is very, very easy to use and efficient. You can also set mp3 files as ringtones, when a SMS is received, as well as for a phonecall.
It will personalize your Treo extremly.
The new version allows you to set a different volume for Call and for SMS Ringtones, it also has a 5-Day trial. You need PocketTunes and a memorycard with music to use this program. Please try the demoversion before you buy the program!