This article explains how to use a landline phone to sign up for a WhatsApp account. It also covers an alternative method if you want a dedicated WhatsApp phone number.
How to use WhatsApp without a phone number?
When you first sign up for WhatsApp, it looks like you need a mobile phone that supports texting. Actually, any phone number should work, since you can receive the verification code via a phone call. Here’s how to set up WhatsApp with a landline:
Start the installation process by opening the app and tapping Agree & Continue on the home screen.
Confirm that the correct country is selected, then enter your landline number and press Next. You may be asked to confirm the number; choose Yes.