When you begin your business using Twillio for sms verification is pretty expensive, I was looking for a free/very cheap service for the beginning.

I can see that Facebook provides - Whatsapp business API and it's unclear if you can already use it to send messages as an individual developer. https://developers.facebook.com/docs/whatsapp/

I can see that Twillio also have a Whatsapp API which costs money.

Is there a way to send Whatsapp messages today ?

Is there other affordable choice to verify new users by sms ?