How to locate a person with his mobile phone

Geographically locating a person through his mobile phone is a service offered by Google Latitude, but also by other companies.
Google's service works in conjunction with Google Maps, the person is located by a red arrow on the map.

To have this system, you must have a mobile sophisticated enough to display the map, which is the case of phones equipped with Java, Android, of iPhone and Blackberry, or devices running Windows Mobile 5.
You can then have the location displayed on your own mobile or a computer.

This system also requires the collaboration of the person to locates, as the list of options on the right shows.
It is therefore a means to locate his relatives, friends ... if they want to!

A similar service is offered by several competitors:

Google's service:

The video on Youtube:

Google Latitude