Caller ID Display is a general term for the feature that shows the caller's phone number on a telephone or smartphone screen during an incoming call. It is positioned as the most fundamental tool for combating nuisance calls, providing information to help decide whether to answer calls from unknown numbers.
For landlines, subscribing to NTT's Number Display service (440 yen/month) is required. The caller's number appears on a compatible phone's display, and call history is also recorded. For mobile phones and smartphones, caller ID display is a standard built-in feature at no additional cost. If the number is saved in contacts, the registered name appears instead of the number.
Installing nuisance call protection apps (Whoscall, Denwa Navi, etc.) on smartphones further enhances caller ID functionality. These apps cross-reference incoming numbers against cloud databases in real time, displaying warnings such as "suspected nuisance call," "sales call," or "fraud reported" alongside the number. Even for numbers not in your contacts, the business name or industry may be displayed.
Caller ID display has limitations. Withheld number calls show only "Private Number," making it impossible to identify the source. Some international calls and IP phone calls may also fail to display correctly. More seriously, caller ID spoofing can display real bank or government numbers. Since the displayed number is not always accurate, it is dangerous to fully trust caller ID alone. For suspicious calls, rather than calling back the displayed number, verify the official contact on the organization's website first. See How to Handle Unknown Calls for specific decision criteria.