Building with simple ADT system already installed... keypad at front and rear doors, 2 door break switches and 1 motion sensor. Any idea what ADT might charge per month to monitor this system ? Also, might it be possible for it to be rigged to a cell phone instead of via the usual wired business line ? I don't really need a wired line and I hate to pay $55 a month (min business rate) just for the freakin phone line.