Mobile phones, like any electronic apparatus having two parts: the hardware (keyboard, screen, speaker ...) and software (display, read messages, calendar, games ...).
There is specialized software, the operating system that controls other applications, but mainly manages the hardware devices. In computers we can clearly distinguish the operating system (Windows, Linux, and Mac OS) from other programs.
In mobile phones, this was initially totally transparent to the user. The phone could make a very limited number of things that were already factory installed. Although the functions were more or less common, each mobile was different because it was handled with each manufacturer's own software, which could be very different from another.
Later we were allowed to install small mobile applications, especially games in Java. There we began to differentiate itself from the mobile software and we could install. Even as the mobile operating system still depended...