A spam call filter is a feature that cross-references incoming caller numbers against a database, displaying warnings or automatically rejecting calls identified as potential nuisance calls. Unlike manually setting call blocking, it can detect unknown nuisance numbers using databases of millions of entries.
Carrier-provided services include Docomo's "Anshin Security (Nuisance Call Prevention)" (220 yen/month), au's "Spam Message/Call Block" (included in Phone Basic Pack at 330 yen/month), and SoftBank's "Nuisance Call Block" (330 yen/month). All leverage nuisance call databases from providers like Tobila Systems.
Among third-party apps, Whoscall is representative, identifying callers in real-time during incoming calls and displaying warnings for nuisance calls. The free version provides basic identification, with the paid version adding automatic blocking. Denwa-cho Navi also has rich domestic user review data, with strengths in detecting domestic sales and scam numbers.
Spam call filters are not perfect and may incorrectly block legitimate calls (false positives). A newly opened store's number might be registered as a former nuisance number, or a call center number might be flagged as telemarketing. When expecting important calls, consider temporarily relaxing filter settings. Most filter apps record blocked numbers in call history, so regularly checking for false blocks is a good habit. Review effective usage in spam call database usage guide.