To install WhatsApp on your phone you have to first check if your device is capable of running WhatsApp Messenger. Please consult the page “Does it work on my phone?” first.
Installing WhatsApp on an Android device
To install WhatsApp on an Android device please visit the Android Market or Google Play and search WhatsApp. Select the app and install it on your phone.
Installing WhatsApp on an iPhone
Go to the App Store on your phone and search WhatsApp. It will install automatically on your phone. Alternatively you can download the app through iTunes and connect your phone to your Mac or PC to install it. If you have bought WhatsApp before you can download it for free again with the same iTunes account.
Installing Whatsapp on a Blackberry
Go to the Blackberry Appworld on your Blackberry device. From here search WhatsApp and download the app with the shown steps on the screen.