My mobile phone is some years old and rarely rings; in fact, it's rarely even on, as most calls I receive are from recruitment agents with that "special" opportunity. I rather doubt it knows what an MP3 is.
For some reason, the second thought I had was contemplation of Boccherini's Minuet (from The Ladykillers - that's the original, of course) as a ringtone (my first thought, understandably enough, was of homicide). I suppose other classical soundbites could work - The Ride of the Valkyries, for instance, or perhaps something from The Rite of Spring.
And for text messages, of course, it would have to be Willie Rushton crying out Mornington Crescent!.