Functionality:

• ListEntries - List all entries in the phone book or those that match on a specific surname
• CreateEntry - Create a new entry to the phone book
• RemoveEntry - Remove an existing entry in the phone book
• UpdateEntry - Update an existing entry in the phone book

Future enhancements:

• Multi-tenancy - implement different phonebooks for different users
• Authentication - validate username/password and use them to determine which phonebook belongs to the current user
• Improve persistent storage - use relational database
• Allow order of listed entries to be specified
• Allow more than one number per contact