Truecaller: naming a stranger before the second ring

How caller ID and spam detection work for hundreds of millions of phones: 500 million+ users and 411.1 million daily users outside iOS (Q3 2026, preliminary), 68 billion+ spam calls identified and blocked in 2025; a read path where the phone answers first and the network is asked once, with a deadline, for a precomputed serving record; hash-partitioned, regionally replicated records with hot numbers kept as cache copies that are overwritten, never deleted; a crowd-written directory scored by weighing evidence (call proof, reporter trust, distinct reporters) in a stream, with weights from a daily batch; a signed regional spam list on the phone as a base plus deltas; private iPhone lookups through an Oblivious HTTP relay, Privacy Pass tokens and PIR over sharded data in memory; and the consent question, with Truecaller's statements, its critics, a 2026 Lagos ruling, India's DPDP Rules, unlisting within 24 hours and lineage on every name.