WhatsApp can find which of your friends are using WhatsApp quickly and easily. WhatsApp reads your contacts' phone numbers from your phone's address book and automatically adds them to WhatsApp. Your contacts with WhatsApp accounts will automatically appear in the favorites screen on your Windows Phone.
If you would like to add a new contact to your favorites screen on WhatsApp, simply enter their name and number into your Windows Phone address book.
When you are adding contacts who live in other countries, make sure that you enter their phone number in the full international format:
If someone who is not saved in your address book sends you an initial message in WhatsApp, you will have the option to save their contact information by tapping add to contacts.
Alternatively, if you are chatting with an unsaved contact and want to save their number, follow these steps:
If your contact does not appear in the favorites screen, you may need to refresh your favorites list:
Learn how to add contacts on: Android | iPhone | Nokia S40 | BlackBerry | Nokia S60 | BlackBerry 10
Cheers,
WhatsApp Support Team