http://wiki.freepbx.org/display/HTGS/Installing+FreePBX+on+Debian+Wheezy
Initial System Setup
Install sudo

apt-get install sudo

Configure your root password.

sudo passwd root

Switch to the Root User

sudo -i

Update Your System

apt-get update && apt-get upgrade -y

Install Required Dependencies

apt-get install -y build-essential linux-headers ( Read more... )