The Apple iPhones seem to be very efficient in every respect, except for the fact that they do not ever come with a dual-SIM feature. This may or may not be a huge factor for many people, but there are a select few perhaps,s who would like to use just one phone for their work as well as their personal calls/messages/emails.
Kickstarter has the perfect solution to your problems, if you are in the latter category of users. They aim to launch a product called Piece that allow the iPhone 6 and other older iPhone models to handle two different SIMs on one phone.