How about the sound of tarzan's call as he swings through the jungle?
You know' aaahahahahahahhhhhhhhhhhhhhhhhahhhhhhahhhhhhhhhhhhhh'
Legally, you have to pay for the copyright for a re-recording of a 'musically significant portion' of an existing piece of music, so all the songs mentioned so far can't be free, unless they are out of copyright, which happens 70 years after the author's death.
This rules out almost everything I can think of that's Swing related... Even something really old, like Swing Low Sweet Chariot (written in 1919, author died in 1949) has many years of copyright remaining. Sound recordings have a 50 year limit on them, but unless we find a swing band recording from before 1945 that we all like, I don't hold out much hope of a good source there.
Really, it boils down to making a new piece of music, 30 seconds long, then converting it to phone compatible formats, and then somehow arranging delivery to phones. I've made a few of my own ringtones (I have a little recording studio here, and wanted something vert distinctive, so I can be 100% sure when I hear it, that it's my phone and nobody else's), and it's not too hard to do if your phone plays mp3s.
I'm sure we have enough homegrown talent round here to make an exclusive tune, which we can share at munches, or offer to the new owners to do all the difficult stuff that supplies the results to non mp3 phones, via wap, etc.
I'm more than willing to take a stab at composing a tune, but i'm not sure I'll be able to come up with something that everyone will like, especially as the last time we had a 'what music do you like' thread, everyone from Nine Inch Nails to Donny Osmond was mentioned!