An old-model Fujitsu flip phone has a devoted fan base in Japan because of its enhanced privacy features. It allows you to designate certain contacts as private, and, according to the Wall Street Journal
, "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."
This makes the phone perfect for philanderers, and has earned it the nickname "uwaki keitai" or "infidelity phone." Apparently no other phones offer such robust privacy features. For which reason, people are sticking with their old flip phones rather than upgrading to new models.
I can see a flaw in their strategy. Now that the phone is known as the phone-of-choice of philanderers, having one is a sign of what you are.