What mobile phone were you using four years ago? It couldn't have been an iPhone because they didn't exist. Chances are, you were using a Nokia. Are you still using one now?

Once upon a time, if you had a Nokia, you simply upgraded to another Nokia. There was nothing better around. Then along came Apple with its iPhone and in one fell swoop, everything changed.

Why operating systems count

But what is it exactly that makes an iPhone very different to a Nokia, or a Samsung, or an HTC, or a BlackBerry? Besides the way the phone physically looks, what sets them apart is the software running them.

This software is known as the "operating system" or simply OS. It's what you look at every time you need to do anything on your phone. It's the way you move through menus, the way you change settings, the way you look at your photos, send an SMS or play music. It's the way a phone "feels" to use.

Given the OS basically drives a phone, it's funny that most people have absolutely no idea what operating system is running on their phone. All they know is that some phones are easier to use than others, that some feel more intuitive.

So what mobile phone will you be using four years from now? According to data from international research firm Gartner, almost 30 percent of us will be using an operating system that last year had just 1.8 percent of worldwide market share.

Android invasion

The OS is called Android and it was developed by Google. It can be found on various phones such as the HTC Desire and Samsung Galaxy S. Like the iPhone, it relies on a simple layout of colourful icons on a large touch screen. You can also customise Android and tweak it to run your choice of programs called "apps" and "widgets".

Apple's iPhone runs an OS called iOS. Apple owns it and you'll only find it on Apple devices. Gartner believes by 2014, phones running iOS will account for about 15 percent of the worldwide market.

What about the rest of us

Nokia, which still sells the most mobile phones worldwide, uses an OS called Symbian. Symbian is now considered a bit of a dinosaur compared to the vibrant and dynamic platforms of both Android and iOS.

Trudging through clunky, convoluted menus is over. We now have alternatives. The main advantage of Symbian, however, is that it can be found on lots of cheaper handsets; not everyone can afford a $719 iPhone.

Gartner says Symbian phones will account for around 30 percent of the market in 2014. It sounds impressive, but it's significantly down from the almost 50 percent slice it commanded last year.

Shrinking share

Research in Motion, the company behind BlackBerry, is predicted to have around 12 percent share in four years' time. That's down from almost 20 percent last year, which still places it streets ahead of Microsoft.

Microsoft's mobile phone OS was known as Windows Mobile and was pretty much designed to look and work like a desktop PC. It heavily targeted business users rather than the average mobile phone user, and enjoyed reasonable traction in this market until iPhone and Android started muscling in.

New beginnings for Microsoft

But for Microsoft, it's out with the old and in with the new, starting with the name. Windows Mobile (WM) is now Windows Phone (WP) and it was launched on October 11. The first version of WP is called Windows Phone 7 and it can be found on handsets such as the HTC 7 Mozart and Samsung Omnia 7.

Given Symbian, iPhone and Android handsets have had a pretty decent head-start, Microsoft will be playing serious catch-up in this market. And the news gets worse. Gartner expects Windows Phone to have less than 4 percent market share in four years' time, placing it right down the bottom of the ladder.

When it comes to buying a mobile phone, do you consider the operating system? Or do you have other priorities?

Roulla Yiacoumi is an Australian technology journalist with 15 years' playing experience under her gadget belt. Follow Roulla on Twitter.