A USB host shield for the Arduino is needed to connect to an Android hand set. You’ll be able to send and receive strings via the terminal, with support for carriage return and life feed characters.

1) A USB micro-controller board that is based on the Arduino Mega2560 and Circuits@Home USB Host Shield designs (now referred to as the ADK board), which you will later implement as an Android USB ...

Arduino explains a little more : “the Arduino USB Host Shield is based on the MAX3421E, which is a USB peripheral/host controller containing the digital logic and analog circuitry necessary to ...

The Arduino, Bluetooth module (check your specs, some HC-05, and HC-06 may come on a breakout board expecting 5V), and USB Host shield all run off of 3.3V, but devices you want to plug into the ...