Finally a interesting hack using NCF (Near Field Communication which is besides closer to the market reality): Janne Jalkanen developed a NFC powered presence application:

I took two NFC tags (essentially very small memory cards with a radio that can be read/written from up to a few centimetres), wrote the URL of my web service on both of them (using the ServiceDiscovery app included), and wrote a little JSP page that handles the interfacing with my blog.

Then I stuck one tag on my work monitor, and another one at home. Now I can just touch one of these tags with my phone, and a few seconds later (some delays are involved with starting the Java midlet and connecting to GPRS) the little box on the right changes to show my location. Voila: NFC-powered presence.

This is in essence no different from doing a Trackback ping; I'm just doing it by touching something with my phone. Not traversing menus, not using the keyboard, not even glancing the screen.