So what has some mobile phone users in Japan unwilling to let go of an old, outdated feature phone? It's not nostalgia, and it's not some sort of ironic fashion statement either. If you said "adultery," then winner, winner, chicken dinner, you're right on the money. The Fujitsu F-Series flip phone is strangely popular in that otherwise magical land of advanced technology, thanks to a passionate userbase of philanderers.

Here's the deal: Apparently a lot of Japanese users have been caught redhanded when their spouses or significant others snoop through their smartphones and spot strange or recurring calls. And so, to better conceal them, some users are resorting to these "infidelity phones," as they're nicknamed, because they make it easy to hide calls and texts from specific contacts.

The obvious question is why those users don't get a smartphone and simply rename that contact entry in their addressbooks. Oh, but that doesn't hide the number. The spouse could simply hit those digits and find out the truth. The other solution might be to lock down the device with a pin code or pattern unlock. But in some households, that can create more suspicion than anything else. "With Fujitsu's 'privacy mode,' they can't see that information at all," explains one Japanese blogger who specializes in picking up women. "The key is to give off the impression that you're not locking your phone at all."

With Fujitsu's F-series, a user simply sets a contact as private, and alerts from that person show up as a subtle shift in color or minor alteration in the icon stack (where the battery indicator sits). And if the user is unable to answer the phone — say, because he's sitting next to his wife — he can ignore the call and not worry about it ending up in the log. When he's alone and ready to check his messages, a few quick keystrokes shuts down privacy mode and conjures up those calls, messages and voice mails.

It's every suspicious wife, husband or romantic partner's worst nightmare. Lucky for them, the phone is limited to Japan only — and maybe not even there for much longer. Like everyone else, Fujitsu is phasing out feature phones in favor of smartphones. While the company did port some of the privacy features, they rely on a standalone mail and contacts application, not the native apps. This is what has cheaters across Japan clinging tightly to existing F-Series phones. For its part, the company is working hard to bring more secure features to its smartphones, to help out this fervent userbase.

Well, this is certainly one type of lifestyle-oriented device. Unfortunately, it makes me cringe at the general baseness of mankind. But hey, I'm not here to judge, merely to inform. And so, against my better instincts, I'm going to share the grace note that The Wall Street Journal used to capped its story on the matter: If you're an Android user looking for similar utility, the $4.99 Call and Text Eraser app may have what you need.

I actually got wind of CATE a while back on a TV show called Shark Tank. (If you haven't seen it, you totally should, especially if you're an entrepreneur. This and Dragons' Den are must-see television for any startup founders or wannabes looking to jumpstart their operation with investment dollars.) After pitching the app, Neal Desai wound up getting $70,000 from the sharks. While some of them refused to fund something so ethically disconcerting, two of them, Daymond John and Kevin O'Leary, took the bait and even offered $20,000 more than the $50,000 Desai originally sought — proving that even a cheater's hushed tones can still scream "money."

Here's a clip from Desai's appearance on Shark Tank. Enjoy before ABC gets wind of it and pulls the vid down.

So if you need something to bridge the gap in security — and cover your butt — you've got an alternative. And you don't even need to go to Japan or downgrade to a flip phone to get it.

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