Google has announced a new service called "Latitude"

Google Latitude lets you see your friends on a map on Google Maps for mobile and iGoogle. Use Latitude to plan an impromptu meetup, see that a loved one got home safely, or just stay in touch with friends. www.google.com/latitude

See where your friends are on a map with Google Latitude. Latitude is a new feature for Google Maps for mobile and an iGoogle gadget, it supports

It is initially available for the BlackBerry and devices running Nokia's S60 or Microsoft's Windows Mobile software, with a Android version to follow.

In a list of phones Latitude supports, support for iPhone and iPod touch is listed as “Coming soon! … via the Google Mobile App”, at least in the United States.