Use ArduActivate to trigger your Arduino with you iPhone's GPS. This app works with the unmodified demo of tinywebserver of Arduino with Ethernet shield. It triggers the digital out when you are in a circle range from your home or wherever you want. You define a circle center (base) and a radius, and when you are close enough to the base, the iPhone sends to Arduino the activate command. Useful for example for opening gates when you're coming home and don't what to use your remote... as when you're in your motorbike... For more info, pictures and video visit: http://www.totemc.com/home/arduactivate
Istruzioni in italiano qui: http://www.totemc.com/home/arduactivate/arduactivate-ita-en
"Continued use of GPS running in the background can dramatically decrease battery life."