WhatsApp is a smartphone messaging application that is available for the iPhone, BlackBerry, Android and Nokia. The application allows you to send and receive instant messages across platforms over a Wi-Fi or cellular data network. If you have installed the WhatsApp on your smartphone, you can add additional contacts to the application by adding the contacts to your smartphone's address book or contacts application.
Open the address book or contacts application on your smartphone.
Select the option to add a contact. If you don't know how to add a contact, consult the owner's manual for your smartphone.
Add the contact's name and mobile phone number to your smartphone's address book or contacts application. The phone number must match the phone number associated with the user's WhatsApp application.
Ask the person you added to your smartphone's address book to download and install the WhatsApp application on their smartphone. The contact's smartphone number must match the number you added to your address book or contacts application in Step #3.