How does the Audi Maintenance Plan work?

I am considering buying a used 2003 Audi A4 3.0 and heard that I may be able to get free oil changes and service through my local Audi dealer. Does Audi have such a plan and if so, how long is it good for?|||Unless you are buying new the free maintenance prob. wont apply. Some dealers may offer it with used cars they sell, but I'm sure it's rare.