I have backorders enabled, rather than the item showing in stock I would like it to display "Available to Order" so that customers have advanced warning ahead of checkout that the product may not be initially available.
Is this possible with the current configuration options or does this require a module?
You can use extension for this
Magento 2 Pre Order extension provided by mageplaza
Find helpful ?Consider Giving Kudos to this post.
Problem solved? ClickAccept as Solution!
Yes there is Magento2 Pre Order Extension will allow you to alert the customer with text available to buy when becomes in stock. Kindly refer the above link.
If my answer is helpful, then hit kudos and accept as solution
Sorry, I think you have misunderstood.
This is not notification by SMS.
Example. Out of Stock items say "Out of Stock", In stock items say "In Stock". I would like items that are 0 quantity but have back orders enabled to say "Available to Order" by the add to cart button.