With the waapp.me app, you can connect to the WhatsApp Messenger service without having to save the numbers in your phone book. You don't need to save the phone numbers because the service doesn't require you to do that.

The service is available for Android. 

How to use the app:

Open the waapp.me app, enter the number and click "Connect".

You will be connected with the target user.

You will be given the option to start a chat or to send a pre-set message.

If you choose to start a chat, you will be given the option to save the number to your contact list or to continue without saving the number.

You will also be given the option to end the chat.

The app will automatically detect the country code of the target user.