Price: 99c in the App Store for iPhone/Free from BlackBerry App World

[Download for iPhone]
[Download for BlackBerry]
[Download for Nokia S60]

The WhatsApp iPhone application was recommended to me by a friend who, get this, makes use of a Blackberry and I really think that this application needs talking about. It's an iPhone/Blackberry application –somewhere between a short messaging system and instant chat but not quite either – that allows you to send messages across networks to friends who has the same application with the help of your current internet connection (Edge, 3G and Wi-Fi) using Push notification.

To get started with this application the obvious first step is to download the app. Once it has been installed you can start it up and follow the easy on screen instructions. What's really great about this app is you don't have to register a username, but rather, it registers your telephone number on its database and there's no need to sign in or out as it's not an instant messaging service.

After you've been "registered" (it really is a painless process) the app runs through your contacts list and adds other WhatsApp users to your Favourites page; alternatively you can also see other WhatsApp users in your Contacts page – there'll be a little chat bubble next to that persons name with a status message.

If you need to invite a friend to use the application you can easily send them either an invitation via SMS or email, both of which will include a link to the respective stores where they will be able to purchase and download the app.

To actually exchange messages is fun and seamless provided that you have one of the internet connections mentioned previously (EDGE, 3G and Wi-Fi) and I also found that sending and downloading pictures and photos are even faster than a normal MMS. Note: this app will work on all iPhones running 3.0 and above.

The app keeps all your current and past conversations on one page in one continuous line, grouped by name, so organization and upkeep is minimal as far as deleting older messages go and the Broadcast Message on the Chats page allows you to send one message to all of you WhatsApp contacts in one go.

On the Settings page you can check the network and system status, check your usage, get help and select and set options such as the screen auto lock or landscape mode. You can also change your chat settings; like your chat wallpaper, sounds and vibrate options.

All-in-all I found this application to be a welcome change to the many other chat and SMS services out there that are available for download, and if you have either and iPhone or a Blackberry you will find that navigating this app isn't frustrating or hard.