Apple’s developer documentation says Live Caller ID Lookup lets a third-party caller ID app check an incoming call against the app maker’s server for known spam numbers, then show the result on the incoming call screen and in your recent calls. Apple says it does this while hiding your IP address, your identity and the incoming phone number from that server, using three separate privacy layers.
That is an unusual promise for a spam blocker, since the obvious way to build one is to send every incoming number to a company’s server. Here is what Apple’s documents say happens instead, and how to make sure a supported app can actually do its job on your iPhone.
What Live Caller ID Lookup does
When your iPhone receives a call, the system, not the app, talks to the provider’s back-end server to retrieve caller ID and blocking information. That information then appears on the incoming call screen and in the device’s recent calls.
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Apple lists three ways the feature protects you:
- It hides your IP address using Apple’s Oblivious HTTP.
- It uses anonymous authentication with the Privacy Pass protocol.
- It hides the incoming number using private information retrieval, or PIR.
Each layer covers a different gap, so it is worth taking them one at a time.
Layer one: your IP address stays hidden
Oblivious HTTP routes each request through two relays hosted by different parties. According to Apple, the first relay removes your IP address from the request and can’t see the destination address. A third-party provider hosts the second relay, and Apple says this removes the IP address before the request reaches the server.
In plain terms, the company running the caller ID service never sees where the lookup came from, and the relay that does see your address doesn’t know which service you are asking.
Layer two: the server knows you signed up, not who you are
The provider still has to confirm that a lookup comes from someone registered with its service. Live Caller ID Lookup handles that with Privacy Pass, which Apple says lets the provider authenticate registered users “without sharing their identity or linking the client’s identity to the query.”
Apple describes the sequence like this. The app on your iPhone first authenticates you with a temporary ID and receives a long-term token. The app hands that token to the system. The system then runs multiple round protocols with the provider’s server and receives several private tokens it can use to make authenticated anonymous queries.
Two details matter for users. Apple says the provider’s server doesn’t learn which user token the system has. And the app itself only takes part in that first sign-in step. It doesn’t know the private tokens or the phone numbers being looked up, because the system controls them.
Layer three: the number itself stays hidden
Hiding your identity is not enough on its own, because the query still contains the number that is calling you. Apple says Oblivious HTTP and Privacy Pass “don’t hide the query itself,” which is where PIR comes in.
Apple defines PIR as a cryptographic protocol that fetches data for a particular keyword from a hosted database “without revealing the keyword to the server.” Here the keyword is the incoming phone number. The provider has to run a PIR server on its database and handle all of the encrypted queries. For developers, Apple points to its Swift homomorphic encryption library and a Live Caller ID Lookup example on GitHub.
How to turn on a caller ID app on iPhone
A caller ID app can only help once it is switched on in Settings. Apple’s iPhone User Guide for iOS 27 lists these steps:
1. Go to the Settings app on your iPhone.
2. Tap Apps, tap Phone, then tap Call Blocking & Identification.
3. Turn on one or more of the options. Call Identification apps uses supported caller ID apps to identify callers. Business Call Identification uses Apple Business Connect or your carrier.
If an app asks you to enable it, that is expected. Apple’s developer documentation says an app can check whether its extension is disabled and open Settings so you can turn it on, because the extension needs to be enabled before the system can talk to the provider’s server.
Common pitfalls
- It is not the same as the Spam filter. In Settings, then Apps, then Phone, the separate Spam switch silences calls your carrier identifies as potential spam or fraud and moves them to the Spam list. That relies on your carrier, not a caller ID app.
- Repeat calls may not trigger a new lookup. Apple says the system caches responses for a time the provider sets per entry. If the same number calls again before that cache expires, the system uses the cached result instead of making another PIR request.
- Not every caller ID app uses it. Apple says the extension requires Apple’s relay servers and endpoint validation from Apple, and developers have to submit a request to use it. Check the app’s own description before assuming it works this way.
What developers need
For app makers, Apple says the extension is added in Xcode through File, then New, then Target. Its information property list needs a top-level NSPIRConfiguration dictionary with two keys, PIRServerURL and PrivacyPassIssuerURL. Apple’s documentation lists the supporting API from iOS 18.0 and iPadOS 18.0.
The full breakdown is in Apple’s developer article, Understanding how Live Caller ID Lookup preserves privacy. If you would rather stop unwanted calls with the tools already built into iOS, our guide on how to block spam calls and texts on iPhone covers those settings.
