The Arduino BT is an Arduino board with built-in bluetooth module, allowing for wireless communication.
Arduino! Without wires! Plunk it down, turn it on, pair it to your bluetooth-enabled host, and you're tapping directly into your Arduino like it were cable tethered.
Because it is "mobile friendly" it offers the handy feature of a DC/DC converter that lets you run your batteries down to as low as 1.2V and still keep your Arduino alive. (But it is quite sensitive to over and reverse voltages - keep it below 5.5V!).
The Bluegiga WT11 bluetooth module can be configured with commands set over the serial port from the ATmega168 (see the iWrap user's guide for details).
For specific details on the WT11 Bluetooth Module, check out the Bluegiga website at www.bluegiga.com