The XBee node -- a popular implementation of the Zigbee protocol of 802.15.4 wireless devices -- is not by any means the cheapest way to create a wireless link to an Arduino-based (or similar) project, but it certainly seems the simplest.
And thus this Instructable -- a rather long telling of a rather simple project.
Step 1: Take it Apart
Pry out the four rubber feet on the bottom and remove the four screws there. Pull the dome and surround off. Unscrew the two screws holding the circuit board -- keep the screws in order; the screws holding the board are the long ones. Pull out the spring plate. Unscrew the last four screws and remove the last big chunk of plastic.
For this project, we need to tear down a little further. De-solder all the components on the circuit board. Desolder and discard the wiring harness. Work the speaker free gently with a screwdriver, cutting some of the glue first with a hobby knife if necessary.
And now we come to the first picture (seriously, if you can't take apart a plastic toy without pictures, you probably shouldn't be trying to wire up an XBee node.) To get a nice space for the parts I wanted I needed to remove the lump of plastic in the center of where the speaker sat. My Dremel made short work of that.