Can you link any landline phone number to WhatsApp Business?

It is possible to link any number of landline phone number to WhatsApp. However, you do need to enter a code that is sent to you over the phone by a computer voice. 

Phone forwarded:
If you have forwarded your landline number, you may not be able to receive the code. In this case, you must first disable call forwarding before you can link your landline number to WhatsApp. 

085 number:
In principle, WhatsApp supports all landline numbers, but unfortunately we sometimes see that an 085 number is not supported. In that case, we recommend using a different number.