I'm working on a Midi controlled Speak and spell to trigger trigger circuit bend sounds with midi notes. I've started this long time ago but now it's working fine (see http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1292582453)
The arduino shield interface works fine and just released the code and schematics. you can take a look at : http://noizeinabox.blogspot.com/ for the development blog or : http://code.google.com/p/noizeinabox/ for the code.
Quick warning if you want to try with your arduino, DON'T CONNECT your arduino to the speak and spell directly because the speak and spell work with different voltage (+5V and -15V). Not sure your arduino will like it.
For now, the functionality is very basic but it works.