I've recently read j-dash-bi latest paper and it's very nifty: Telebeads: Social Network Mnemonics for Teenagers by Jean-Baptiste Labrune and Wendy Mackay (IDC2006). It's actually a participatory design paper that describes how they designed a curious artifact:

This article presents the design of Telebeads, a conceptual exploration of mobile mnemonic artefacts. Developed together with five 10-14 year olds across two participatory design sessions, we address the problem of social network massification by allowing teenagers to link individuals or groups with wearable objects such as handmade jewelery. We propose different concepts and scenarios using mixed-reality mobile interactions to augment crafted artefacts and describe a working prototype of a bluetooth luminous ring. We also discuss what such communication appliances may offer in the future with respect to interperception, experience networks and creativity analysis.

The ring addresses two primary functions requested by the teens: providing a physical instantiation of a particular person in a wearable object and allowing direct communication with that person. (...) We have just completed an ejabberd server, running on Linux on a PDA, which will serve as a smaller, but more powerful telebead interface

See the bluetooth telebead ring and how to associate the ring and a contact image:

Why do I blog this? I like this idea of "mobile mnemonic artefacts" as part of a situated and cognition framework: that's an interesting instantiation of communicating objects. Besides, the paper is full of good references about such devices.