The Extra Button module is available for the product page and product listing (grid/list views). Up to two buttons may be activated at the same time.
Link button acts as a normal button which can point to any link. This includes opening Popups, such as one with a contact form in it which can be used for enquiries, or any other popups with any content.
Buy Now button will automatically add the product to cart and proceed to checkout.
Any button can perform either function, to change the order they are rendered simply change the name and function of each button.
See Product Assignment for more info on how this concept works. You can assign modules to all products, individual products or a custom set of products matching a certain criteria or rules.