By Dan Simmons
From maps to playing music, mobile phones today are much more than just devices for talking while you are walking.
Online stores by big brands have come up with tens of thousands of applications to enhance the handset experience.
From magnifying glasses to apps that record calories burned, users can buy extra functions for their devices.
Mobile operators are also starting to get in on the act, and are expected to bring a new dimension to their services.
Phillip Stubbs, director of products at Airwide Solutions, said messaging, voicemail, and voice calls could one day be added to other applications.
"These types of services can be integrated into your favourite social networking sites so you can be talking to a friend and that can be published directly.
"It really just makes your entire communication experience a whole one, rather than just a small number of parts put together," he said.
Applications for all handsets, and not just smartphones, have been around for many years on lots of different sites.
For instance, Getjar and Handango have tried to collect them all together - but sites like these have not been promoted by phone makers so users have had to find them for themselves.
Downloading apps to the handset has not always been straightforward either.
Often users have had to download them to a computer, and then transfer the files to the handset to be installed.
Now most smartphones download apps straight to the handset.
Below is a list of some of the better known application stores on the web.
APPLE APP STORE
The Apple app store has around 50,000 applications which have mostly been created by independent developers. As might be expected the applications are only for the iPhone and iPod Touch.
Each self-contained bit of software has been produced to carry out a specific task.
For instance, FStream is a little program that streams radio stations to the iPhone, and lets the user record what they hear.
While Email 'n Walk enables the user write an e-mail while using the camera to see where they are going - so no bumping into lampposts.
Nokia's Ovi store is two months old
Nokia's Ovi store not only offers apps, but also helps the user sync and share content with their friends.
Ovi comes preloaded on the Nokia's N97, but for other models the shortcut can be downloaded by visiting the store on the mobile phone.
The store is only two months old but Click found around 600 apps, with about a third of them being free.
Unlike the iPhone, users can shop around on other sites as not all the apps for Nokia handsets are here.
On the popular N95, apps download straight to the Apps folder. The user needs to sign up for an Ovi account and make purchases with a debit or credit card.
One cheeky app spotted was the potentially useful "choose your background noise" app for use during phone calls.
Research in Motion, creator of the BlackBerry, opened its App World store in April 2009. Access to it is by downloading a link to the handset from its website.
There are half a dozen apps featured daily out of around 1,200 offerings, but the free and paid-for apps are unhelpfully mixed together.
Users need an online PayPal account to make purchases, and downloaded apps pop up in the phone's download folder.
App World only works in North America and the UK at present, with more European countries expected to be added later in July.
The user also needs a handset with either a track ball or touch screen.
There have been complaints that the Blackberry application itself uses up too much of the phone's memory.
If the fledgling official Blackberry site does not have what you want, there are some more established sites to try:
GOOGLE APP MARKET
Android Market is a platform to watch
In 2008, Google dipped its toe into the phone market, not by making handsets but creating the open source Android operating system on which they run.
HTC and Samsung already produce Android handsets which come with Google's own App Market preinstalled.
The market was launched in October 2008 but paid-for apps have only been around since February.
The open source nature of the endeavour has many predicting this could be the platform to watch.
Although the website gives a flavour of the apps available, it is only on an Android phone that users can view the entire range - several thousand in all.
Apps download straight to the phone into the main folder.
Windows Mobile users have one of the largest selection of apps, about 20,000, for any mobile platform. However Microsoft's shop window, Windows Marketplace, remains empty at the moment.
The site simply offers Microsoft's own software to download, but the firm aims to bring many of the apps available here before the end of 2009.
Sony Ericsson opened what will be its own app store, known as playnowarena, to developers at the start of July 2009.
While it has only a couple of apps up there at the moment, there will doubtless be many more for all to play with as developers get to work.