My last phone was a Treo 680. I gave it to my brother-in-law. I'm so accustomed to the SMS ringtone that whenever his goes off I instinctively reach for my phone. 
This has been somewhat of a minor annoyance for me.
So I searched online for a solution.
It turns out that the only format you can find the ringtone in is MIDI, which is like digital sheet music. So it's up in the air as to what type of instrument the MIDI player will default to.
The solution? Pop the MIDI into Garage Band (if you've got a Mac, sorry Win and Linux people!).
Upon playing it in Garage Band the default instrument it chose was 'Grand Piano', which sounded very close to it, but not quite cigar...
After plucking at a few instruments I settled on 'Electric Piano' which to me came closest to the sound on the Treo.
Here's the final result for anyone interested in downloading it:
Alert Swoosh - Electric Piano mp3