WhatsApp Messenger is designed to make SMS a thing of the past. With the app installed, users can send each other free messages using WiFi or 3G.
When you install WhatsApp Messenger, you have to enter your telephone number, then enter a code you receive via SMS. From then the app syncs with your iPhone contacts - anyone who owns the app will have a tab attached. Touch a contact who doesn't have WhatsApp Messenger and you'll be able to send them an invite.
Sending messages is just like the normal SMS service for the iPhone, except of course it doesn't send messages over the phone network. As well as text, you can send images, audio, contacts or even location. WhatsApp Messenger uses push notifications, so you don't have to be signed in to get messages, which makes it just as good as the native SMS service.
WhatsApp Messenger also includes a group chat feature, allowing lots of your friends to talk at once without having to pay per message.
The only issue with WhatsApp Messenger is that it only works between WhatsApp users. It's really good when your friends have it, but if some of your contacts don't own it, you'll be stuck with SMS some of the time! Having said that, if there's one person you SMS a lot, it's certainly worth investing in WhatsApp, as it can save you lots of money!
WhatsApp Messenger works great, as long as you can convince others to start using it too!
For technical reasons, clicking on the download link will take you to iTunes, where you can obtain the program.