Arduino USB host shield

Hi, Quick question to those with experience in using the ArduinoCommander - android application to manage the Arduino through android phones. My project involves using a android phone(galaxy ace 2) to control the Arduino but the phone is not a USB host. I read somewhere that I could buy a Arduino host shield to make the Arduino a USB host but would it then be able to receive commands from the phone?

The point of all this is to make the Arduino commendable through 3G by using the phone to control the arduino and then using a remote desktop to control the phone over 3G from another phone or tablet.

Would appreciate your help :)