Use three SIM cards in one phone
With a Triple SIM adaptor, you can fit three SIM cards into your handset and switch between them using an app, which is automatically installed when you insert the adaptor. There’s no need to reboot your handsets or manually adjust the SIM cards. The app can even be configured to automatically switch between the SIM cards at specified times.
As is, the SIM cards will not operate simultaneously; you need to use them on an individual basis. The video mentions that you could use all three at the same time by using a Bluetooth accessory, although mobile data will not work if SIM cards are used simultaneously. If the SIM cards are used separately, mobile data should work fine on both 3G and 4G.
This is a handy accessory if you have more than one mobile tariff, to take advantage of free text and call bundles, for example. The adaptor demonstrated here is advertised as an iPhone 4G accessory, although it should be compatible with any handset that uses a microSIM. The adaptor connects to the microSIM slot and there are then two extra ports to insert normal sized SIM cards.