The most convenient and fastest application for opening Whatsapp chats by number:

* Intercepts the number from other applications (when opening a phone number) or from the dialer.
* Application size less than 200 kilobytes
* Does not collect or share user data. The app doesn't even have internet access.
* No ads
* Open source and free forever

Whatsapp requires you to save a contact before starting a conversation, which is inconvenient when the contact is only needed once.
If you are faced with such a situation - StartChat can help you.
When StartChat is enabled, it prompts you to open a WhatsApp chat when you call a number.