If you are planning to make Arduino project which you want to control with Android phone via Bluetooth, then this application may helpful lot!
This application I have created for my Arduino project to LED on and off via my Android phone. So I have created two button in this app to LED on/off and one input text box to send any number of alphabet to send Arduino.
For more information about Arduino project and Android application you can visit my blog. Below is the link for project page.