I really, I mean REALLY hate it when wannabe journalist post articles with sensationalized falsehoods in some puerile or ego-stroking attempt to get attention. Absolutely nothing in that cable or Amazon page says, suggests, implies, or shows anything about a "hidden" SIM card slot. In fact, the Amazon page clearly shows it.
Covered does not imply hidden. SIM cards in virtually all phones are located well out of sight, under the battery under the battery cover. Does that imply it is hidden? No. It is just in a protected place. Most USB flash drives have a cover over the USB port. That does not imply hidden. Sure, the name of the product has "spy" in it. But I still see this as the article writer creating fiction rather than reporting the facts. And that is what irritates me.
