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

085 number:
Basically WhatsApp supports all landline numbers, but unfortunately we see that sometimes a 085 number is not supported. We then recommend using another number.