Receiving a call from an unknown number on your phone has become commonplace. The frequency of these solicitations has prompted the French legislator to strictly regulate telemarketing, with dedicated prefixes for commercial calls since 2023 and a major reform planned for August 2026. Identifying the caller behind an unknown number remains, however, an exercise with uneven results, depending on the chosen method and the status of the number being searched.
Commercial Prefixes and the Cazenave Law: The Game-Changing Framework
Since 2023, authorized numbers for commercial telemarketing are limited to specific geographic prefixes and not mobile ones. The prefixes 01-62, 02-70, 03-77, 04-24, 05-68, or 09-48 are explicitly associated with prospecting calls. An unknown number starting with one of these prefixes therefore indicates, with a high probability, a commercial call.
This first filter already allows for sorting without external tools. If the displayed number corresponds to a telemarketing prefix, the question “who owns this number” loses its urgency: it is likely a solicitation.
The next regulatory step is the Cazenave Law No. 2025-594, which will come into effect on August 11, 2026. It will prohibit B2C telemarketing by default in France. Only an explicit and provable opt-in from the consumer will allow a commercial call. This shift will mechanically reduce the share of unknown calls related to prospecting. After this date, a commercial call received without prior consent will become a reportable anomaly.
For those who want to find out who owns a number with Datta, the process remains relevant even within this new framework, particularly to verify if a displayed number pertains to disguised telemarketing or a legitimate contact.
Reverse Phone Lookup: What Works and What Doesn’t
Reverse lookup involves entering a phone number into a search engine or directory to find out the identity of its owner. The principle is simple, but the results are less so.
Reverse Directories and Google Search Engine
Typing a number into Google remains the most common reflex. The engine aggregates results from public databases, online directories, and forums where users report suspicious numbers. For a professional landline or a company switchboard, this method often yields a usable result.
For a personal mobile number, the available data usually does not allow for a conclusion. If the owner has requested to be listed as unlisted with their operator, no reverse directory will be able to display their contact information. This is a structural limitation, not a technical flaw.
Limitations of Free Reverse Directories
- Free databases only cover a fraction of mobile numbers, as registration in the universal directory is not mandatory in France.
- Some sites display partial results (city, operator) and then ask for payment for the full name, without any guarantee of reliability.
- Spoofed numbers do not lead to any real owner, as the number displayed on the screen is not that of the caller.
Caller Identification Apps: Truecaller and Alternatives
Mobile caller identification apps operate on a different principle than reverse directories. They rely on a participatory database fed by their users. Truecaller, the most well-known, claims a community of several hundred million users worldwide.
When a number calls, the app compares it to its database and displays a name or a report (“spam,” “scam,” “survey”) in real-time. For frequently reported numbers, the result is reliable. For a number that is rarely called or never recorded in the database, the app returns nothing.
The Issue of Personal Data
Using these apps involves a trade-off. By installing them, the user generally shares their entire phone directory with the service. This data transfer feeds the collaborative database but raises a question under GDPR: the contacts stored in the directory have not given their consent.
The CNIL reminds us that telemarketing by automated calling is already subject to a prior consent regime for individuals. This framework also applies, by extension, to data collection by third-party apps. Field feedback varies on this point: some users consider the service provided sufficient to justify sharing, while others prefer to avoid this exposure.
Spoofed Calls and Vocal Deepfake: The Blind Spots of Identification
Identifying an unknown number assumes that the displayed number is real. Spoofing breaks this assumption. A caller can display any number on the recipient’s screen, including that of a bank, a public service, or a relative.
Google began in 2024 to deploy a spoofed call detection feature on Android, targeting scams using voice generated by hypervoice manipulation. This technology aims to signal in real-time that a call has suspicious characteristics, regardless of the displayed number.
This type of protection acts upstream of identification: rather than trying to find out who owns the number, the system assesses whether the call itself is fraudulent. This is a notable shift in approach, as no reverse lookup can unmask a spoofed number.
Reporting a Suspicious Number: The 33700 Service
When identification fails or the call seems fraudulent, reporting remains the most concrete recourse. The 33700 service allows you to report by SMS an abusive telemarketing number or a scam. The CNIL and operators use these reports to feed their blocking lists.
- Send “spamvocal” followed by the suspicious number via SMS to 33700.
- The report is free and does not require any third-party application.
- The most reported numbers are gradually blocked at the operator level.
The combination of commercial prefixes, reverse lookup, collaborative app, and 33700 reporting covers the majority of cases. None of these methods is infallible when taken in isolation: reverse lookup struggles with unlisted numbers, apps with rare numbers, and reporting only acts after the fact.
The regulatory framework being established with the Cazenave Law should reduce the volume of unknown calls. However, spoofed calls will remain a blind spot as long as terminal-side detection has not caught up with the sophistication of spoofing techniques.