The best passage in WSJ's story on Japan's "infidelity phone":
"Women may want to check my phone for strange emails or calls when I'm not around. With Fujitsu's 'privacy mode,' they can't see that information at all," he said in an email. "The key is to give off the impression that you're not locking your phone at all."The problem? Those who continue to own these phones, those who do not upgrade to a smartphone, will eventually be exposed as players. The phone will itself say exactly who you are.
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.