I want to make entering billing information on checkout optional, so the user is asked if they require a bill and if so, enter the billing information, and skip it all together if not.
If there was a plugin that achieves this, it would be great. If not, how do I do it?
Nowadays it seems that shorten the checkout process increases the interest of customers to be on site and reduces the no of chance to let customer go. You should try Merge Billing & Shipping Information at checkout for Free. Hope it fullfil your need.
Quick checkout or additional checkout attributes extension solves your problem, please check it in our store. You will be able to add optional fields etc.