No idea on the Arduino BT board.
Depending on what you have, what you want to communicate with, and what bluetooth profile, there are various solutions. Most of the simple solutions involving bluetooth have the bluetooth device as a simple serial device, where you read/write bytes on two wires at an agreed upon speed like 9600baud. If your Arduino has hardware serial ports (like the Mega/Due), you can use them to talk to the board. Otherwise, you need to use Software Serial support to emulate a serial connection (which works on most boards, but not all).
If you are wanting to communicate with an Apple phone/tablet, etc. you will need a bluetooth 4.0 LE (low energy) setup. This reduces the selection quite a bit, and raises the cost compared to Android phones which typically can communicate with 2.1 bluetooth systems. You can find 4.0 LE bluetooth shields out there if you look, for example, seeed studios makes one: http://www.seeedstudio.com/depot/bluetooth-40-low-energy-ble-shield-p-1255.html
If you are using an Android phone that talks to 2.1 bluetooth devices, Itead and Seeed studios both made Bluetooth shields, for example: http://www.robotshop.com/bluetooth-shield-arduino-master-slave.html
. If you live in the USA, you might check Radio Shack. They used to sell the seeed studios bluetooth shields, and it is possible the retail outlets may still have one lying about. I picked up a shield for my Uno from one for about $10.
There are various free and $$ aps on Android phones to talk to bluetooth devices over serial connections. I imagine there are some on the Apple side of the phone divide. I have one "bluetooth controller" that allows me to set up to 9 buttons that when I tap a button, it sends some text to the Arduino. There are others that you can use monitor the connection and send random text as well.
You can also buy the bluetooth 2.1 separately that is not part of a shield. I have this one, and use it on my Teensy 3.0: http://www.ebay.com/itm/HC-05-Bluetooth-Transceiver-Host-Slave-Master-Module-Wireless-Serial-6pin-/221286562520?pt=LH_DefaultDomain_0&hash=item3385b4fad8