A mobile operating system, also known as a mobile OS, a mobile platform, or a handheld operating system, is the operating system that controls a mobile device or information appliance—similar in principle to an operating system such as Windows, Mac OS, or Linux that controls a desktop computer or laptop. However, they are currently somewhat simpler, and deal more with the wireless versions of broadband and local connectivity, mobile multimedia formats, and different input methods.
Typical examples of devices running a mobile operating system are smartphones, personal digital assistants (PDAs), tablet computers and information appliances, or what are sometimes referred to as smart devices, which may also include embedded systems, or other mobile devices and wireless devices. Different people have different needs, as i will now explain to all of you
Iphone - Great for apps and games, you can jailbreak it to unleash is potential (e.g sending files through BT, using 3G for face time, but will void ur warranty). The easy to use and stable software also is a hit with the consumers
Android - An alternative to iphone (less app and games though). Great for iphone haters but still want a touchscreen. Updates for android OS are also coming fast. IMHO, android is greater than iOS overall
Blackberry - for those who like to stay in touch online on the move. Popular with VIP and business men for the encrypted emails. Has also a nice qwerty keypad in all models.
Symbian - for expert user. It takes some time to learn, but once u get the hang off it, god know's what you can do with Symbian OS. Also great for multimedia junkies (natively supports the most multimedia formats). And it does burden the resources on the phone.
So u see guys, there is no point of forcing another guy to buy another phone just because u like or have it.
Reference: Wikipedia
Reference: Wikipedia