Although it's still in Beta, Nokia's Friend View has been updated to fix some bugs and add small enhancements. The updated Friend View for S60 devices lets you run the application in the background and has an Active and Refresh mode as well as a Normal mode.
It also includes what they call a "pling-plung" feature that lets you know when friends are close by.
You can customize the Friend Alerts meeting zone to allow you to see how close your friends should be in getting alerts.

via: Nokia’s Friend View updated, still in beta though » Unwired View

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