You might have one phone for personal purposes and then another one that was provided to you for work purposes. It can be a bit of a pain having two phones weigh down your pants pocket, so why not combine the two phones into a single device? The DuoSIM is a simple device that effectively lets you have two SIM cards associated with the same handset. Two numbers, one phone.
The video embedded below walks you through the installation process, but all you really do is place one end of the DuoSIM into the SIM slot in your chosen phone, and then you can pop both of your SIM cards into the other end of the DuoSIM. You’ll need “a wee bit o’ space between your phone and the battery cover for this to work.”
Another speedbump that you may encounter with the $28 DuoSIM is that the only way you can switch between the two SIM cards is if your phone OS supports this functionality.