The baud rate is fixed at 57600. This is the baud rate used by Firmata. If you want to use a wireless connection I recommend using an Arduino Fio board with an XBee radio (note that you must use the Series 1 radios). You can run these at 57600 baud.

I have posted an Arduino Fio setup guide and a tool to configure the radios here:
Fio Setup Instructions
XBee Configuration Tool