I have been looking over the documentation for the contacts API as well as the SDK function in question (getContacts), and see the issue you are referring to. Since the default return value for the number of contacts is 10, if you don't set that parameter that's all you will ever have returned to you. I'll pass this information on to the docs team with the specifics so that we can provide that information to users.
Jonathan LeBlanc Senior Software Engineer Yahoo! Developer Network