Q:

Can I create a Windows Phone app that runs in the background (Windows Service) similar

I have a project in mind, but what I need is to feed a Web Service as soon as the GPS location changes with the Long and Lat. So basically I should run some kind of "service" in the Windows Phone device that never ends, starts when the phone starts etc....
Thank you.

A:

You cannot background services on the current version of WP7. The next version, Mango, will support background services.
The beta SDK and emulator is available for download from Microsoft, so you can start experimenting already. 
The new version will be released sometime this autumn.

A:

You may want to look at Scheduled Tasks which let you execute background tasks periodically or the ones that may not be periodic. From your description, periodic tasks seem more applicable and are provided by the PeriodicTask class. PeriodicTask executes approximately every 30 minutes. 
To add, yes, they are available in 'Mango' / 7.1, the next version of Windows Phone. 

