In WSM it's possible to create models that call external function in DLLs. I've been using a modelica wrapper to the oscpack library (http://www.rossbencina.com/code/oscpack) that allows sending and receiving simple OSC messages. This makes it possible to communicate with music applications that implement OSC.
I've been using it to send input signals from an iPhone using TouchOsc.
I'm interested in playing with it too, although strangely there doesn't seem to be any way to get audio or MIDI into or out of it, which is a pity. I'm sure it wouldn't be too difficult to add on, since Mathematica has that sort of thing built in.