Challenge

Here are a few challenges that might be fun:

1. Implement a search by name. This should be pretty easy since we have a map of contacts.
2. Implement listing by starting letter. The contact list is already sorted so it should not take too long.
3. Implement paging where only a subset of contact is returned at a time. The design of this feature is not defined, so just make sure that you can specify the number of contacts you want and that you get the first N contacts, then the next N, and so on.