I often get individuals asking – “I want my customers to be able to buy even if I do not have the product in stock. How can I allow them to buy still? And ship once I have it in stock.”
The answer = Turn on Magento’s Back Order capabilities.
Back Order – a business order yet to be fulfilled because stock is unavailable.
To enable backorders, go to:Admin Panel -> System -> Configuration -> Catalog Tab -> Inventory -> Product Stock Options -> Backorders = Allow Qty Below 0 and Notify Customer Edit Product to Qty = 0 and Stock Availability = In Stock
When you add the particular product to cart, the product is added to cart and you will see the following message:* This product is not available in the requested quantity. 1 of the items will be backordered.You can order the product even if it is out of stock. The product will be delivered to you when it is in stock.