TechBitar wrote this Instructable detailing his ANDRUINO, the 2-way Android controller for Arduino via bluetooth:
ANDRUINO is a simple tool to help you control your Arduino (or clone) from your Android phone. It’s both an Android app and an Arduino program. Andruino has a simple Android user interface to 1) control Arduino’s digital and PWM pins 2) send text commands to Arduino 3) and receive data from Arduino over Bluetooth using the ever popular HC-05 Bluetooth over serial module or its siblings.
Andruino should work with other Bluetooth modules with some tweaking but I have only tested it with the HC-05. This is an alpha version that’s running fine on my Samsung Galaxy S2 Plus. Please share your experience running Andruino on your phone.
Andruino: A simple 2-way bluetooth-based Android controller for Arduino – [Link]