Google lattitude

Google's released Latitude, a Maps tool that allows for automatic tracking of friends in real time, using a laptop, Symbian 60, Blackberry, WinMo and soon, iPhone or Android.

Laptops and cell phones (if they are not equipped with GPS) to find a fair level of accuracy with geotagged Wi-Fi and cell phone tower in a database that Google, on their own, perhaps with Streetview photography. Or you can set your location manually. Google said that there is no fixed standard, how often the map updates your location. Rather, they have an algorithm that depends on how often the device is moving, historically, and how much battery your device has left. You can also leave the service completely, and per-user settings, whether certain friends can your location to all, or if only at the city level for accuracy. Google says it may consider useful for family members to find out whether they are in a traffic jam or on the way home. 

Most phones will be able to keep the map location updated in the background. Except the iPhone. What the iPhone users can do, as a work around, is to lock the phone with the Google app running. That'll keep the phone updating until batteries die.

The Blackberry, WinMo and Symbian phones and laptops/Desktops can use Latitude now by downloading the most recent version of Google Maps or hitting Http://google.com/latitude. The iPhone gets it with an updated version of the increasingly powerful Google app, soon, as does the Android powered G1.