You only need to have Whatsapp Messenger installed and you'll automatically have in your contact list all those contacts who are already using Whatsapp too.
Best of all is that it isn't limited to iPhone to iPhone communication, but you can send messages to any WhatsApp Messenger user, no matter if he uses iPhone, Android, Nokia, Blackberry or any other device.
Once you'll have the application installed, you'll be able to send messages as if they were SMS, but for free,Yes we can ssay it is a good way to send SMS for free and use it to chat as if you were using a common IM client.
You can even attach videos, pictures, links or whatever.
WhatsApp is the perfect application for any iPhone user. With no doubt it is a must have.
The application is offered for free, but requires an annual subscription service. Those who purchased the paid version will not have to subscribe, resulting valid payment hereafter.