A phone book is a directory mapping phone numbers to names. From paper directories delivered to every household to smartphone contacts apps, the format has evolved alongside telephone history.
Japan had two paper directories: NTT's "Hello Page" (white pages listing individuals and businesses alphabetically) and "Town Page" (yellow pages by industry). Hello Page was discontinued in 2023 due to privacy concerns, while Town Page continues as an online service.
Smartphone contacts store names, numbers, emails, addresses, photos, and notes. Cloud sync (Google/Apple ID) enables data transfer between devices. However, contacts are a privacy goldmine - be cautious with apps requesting contacts access.
Spam filter apps can identify unknown callers by matching against their databases, displaying business names or "potential spam" warnings even for numbers not in your contacts.