I have TeleNav
Turns my cell phone into a GPS. My maps are all updated automadically every few weeks. I can also put all my properties in it from my desk top. It even alearts me to trafic and askes if I want to be re-routed. And its only $10 a month. There is no special devices. Just download the software to my cell phone and wola
here is it
http://telenav.com/ Check em out. I have had them for about 2 years now. It even finds newer addresses that my Garmin could not.