windows phone 7 - wp7:Is it possible get autometically trigger when my location is changed? -

i trying create tracing application.in application using location tag.

so possible automatically trigger or message on particular event on location change? i.e: know if user has moved in new location. if user has moved trigger specific event application. specific wp7 service can inform application user has changed location , trigger event application?

my concern if user change location @ time want call 1 web service , send location data server.

the feature asking called 'geofencing'. windows phone apis not support out-of-the-box, pretty easy implement yourself. google 'geofencing windows phone', find number of articles one:

http://blogs.msdn.com/b/dragoman/archive/2010/10/13/wp7-code-geofencing-with-the-geolocation-api-and-rx.aspx