>First you must put a GPS in each device

A gps costs under $1 today:

http://www.alibaba.com/showroom/gps-chip-price.html

>Also, the forbidden areas may vary

It's mostly airports that we need to worry about, and they don't tend to change much. Sure, TMA boundaries might vary occasionally, but that's not really much of a worry, because most drones won't be up at 1000+ ft.