You could connect your pda direct, but not without doing some mods....
Looking at the cct diagram, delete the biassing resistor for the microphone, ac couple the output of your pda into pin 3 of the op amp, then play around with the feedback loop until there is a reasonable signal level where clipping doesnt occur prior to feeding the clipping/didode pump network formed by the diodes/caps......A good starting point I'd have thought.....Anyone else got any thoughts ?