Om Malik points to a new phone application called Jaiku that lets your contacts know where you are via phone or web-page. Jaiku call it Rich Presence. They say:
We invented the term ‘rich presence’ to describe the many relevant things a phone knows about you. Rich presence on Jaiku includes an IM-style away line, your phone profile (ring volume, vibrate), location (country, city/region, neigborhood), Bluetooth devices around, upcoming calendar events, and the duration how long your phone has been idle.