Japan's Philanderers Stay Faithful to Their 'Infidelity Phones'
From the WSJ:
Fujitsu's "privacy mode" is a layer of nearly invisible security that hides missed calls, emails and text messages from contacts designated as private. If one of those acquaintances gets in touch, the only signal of that communication is a subtle change in the color or shape of how the battery sign or antenna bars are displayed. If ignored, the call doesn't appear in the phone log.
The changes are so subtle that it would be impossible to spot for an untrained eye. When the privacy mode is turned off through a secret combination of keys, the concealed calls and messages appear, and voice mail becomes accessible.