There are a dozen websites providing this service already. Since they have to sign up each individual restaurant, they cater to specific cities. My favorite is campusfood.com, which provides online ordering for thousands of restaurants in the cities surrounding over 300 college campuses. They had over 100 restaurants in the Philadelphia area when I lived there. The restaurants don't need any special software or even a computer; orders are placed through the website, optionally paid through the website, and the restaurant gets the order by e-mail or fax.