A smartphone or smart phone is a mobile phone with an advanced mobile operating system which combines features of a personal computer operating system with other features useful for mobile or handheld use.hones with screens larger than 5.2 inches are called  phablets . Smartphones with screens over 4.5 inches commonly are moved around in the hand or used with both hands, since the average thumb cannot reach the entire screen surface. Types of screen include LCD, LED, OLED, AMOLED, IPS and others.