Fujitsu's smartphone offerings have evolved dramatically over the past few years, but in Japan, the company's older flip-phone variant remains surprisingly popular — among cheaters, at least. That's the takeaway from a recent Wall Street Journal article, which takes a deeper look at the social phenomenon behind Fujitsu's F-Series, a handset that according to many, offers greater privacy protections for philandering lovers. The key to the phone's success is a setting that automatically hides missed calls, text messages, and voicemails from numbers designated as private — meaning users can maintain illicit relationships without having to field questions from suspicious spouses.

"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," Japanese blogger Bakanabe said in an e-mail to the Journal. "The key is to give off the impression that you're not locking your phone at all."