In short. A call placed with #31# does arrive with no number displayed, but if it rolls over to voicemail, the nature of your anonymity changes: you leave your voice, a date, a time and a duration, in a message the recipient can replay, save and pass on. Withholding your number hides the display, not the recording. A written message stays easier to control.
Information verified on 5 November 2026 on the public pages of Arcep, the CNIL (French data protection authority), service-public.fr, Légifrance and cybermalveillance.gouv.fr, as well as on the support pages of the French carriers (Orange, SFR, Bouygues Telecom, Free Mobile) and Apple's and Google's documentation. This article provides general information and is no substitute for advice from a legal professional.
What does the recipient of a withheld call that goes to voicemail see?
They see a missed call with no number — labelled "Withheld number", "Unknown caller", "Private" or "No Caller ID" depending on the handset and the carrier — then a voicemail notification. And that is where the two pieces of information come back together: the voice message is dated and timestamped, so it matches the withheld call they have just missed.
In other words, withholding your number works on a single level: caller ID presentation. It does not change anything else in the chain. In practice, the recipient has:
- a record of a call with no number in their call log;
- the exact date and time of the call;
- an audio recording if a message was left, replayable indefinitely;
- the length of the message;
- sometimes a written transcript of the message, offered by some visual voicemail services.
A transcript changes a great deal. A voice message has to be listened to; a transcript can be read, searched, copied and forwarded as a screenshot. It turns a fleeting sound into lasting text.
Does withholding your number with #31# protect the content of the message?
No. The #31# prefix (or 3651 from a landline, depending on the carrier) acts on a technical flag attached to the call: it asks the network not to present your number to the called handset. That is all. The path of your voice, the recording on the voicemail platform, the carrier's logs: none of that is affected.
Three misunderstandings come up again and again:
| What people believe | What actually happens |
|---|---|
| "Withheld = invisible" | Withheld = not displayed on the recipient's screen |
| "Withheld = not recorded" | The call still sits in the carrier's data (billing, routing) |
| "Voicemail keeps nothing" | Voicemail is a recording stored by the carrier |
The last point is the costliest. A voicemail box is not a scrap of memory inside the recipient's phone: it is a service hosted by their carrier. The message therefore exists on a platform, with its timestamp, independently of the phone — and it survives the deletion of the missed call.
Is a voice an identifying piece of data?
Yes, and that is exactly what withholding your number does nothing about. The CNIL points out that a voice constitutes personal data as soon as it allows a person to be identified, directly or indirectly. In practice, someone close to you will recognise you in two seconds: an accent, a verbal tic, a laugh, a way of breathing.
And identification does not come from the timbre alone:
- background noise (an office, a car, a station, children, a television, church bells) places or contextualises you;
- vocabulary and phrasing point to a narrow circle;
- the time of the call cross-references a known schedule;
- one detail mentioned in the message (a first name, a place, an appointment) is often enough to blow your cover.
So if you call with your number withheld in order to stay anonymous and then leave a voice message, you have simply swapped one identifier (the number) for another, far richer one. A number is a line to check; a voice is a person. That is why a written message — including an anonymous SMS that can receive a reply — is generally easier to control than a call: the text says only what you decided to put in it.
Can a withheld call be traced by the carrier and the courts?
Yes. That is the central gap between "anonymous to the recipient" and "anonymous full stop". Withholding your number prevents it from being displayed on the called phone; it does not prevent the carrier from knowing which line called which line, at what time and for how long. This traffic data is retained and can be requested as part of judicial proceedings, under the conditions set out in the French Post and Electronic Communications Code, available on Légifrance.
The practical consequence: if the recipient files a complaint, a withheld number is not a wall. What they cannot obtain themselves — identifying the caller — a judicial authority can request from the carrier. The service-public.fr pages on harassment and malicious calls describe this route: complaint, formal request, identification.
Withholding your number is a presentation option, not a right to impunity. As soon as a message is received as threatening, persistent or malicious, anonymity becomes a circumstance in the case file, not a protection.
The same reasoning applies to written messages: we set it out in detail in our article on the legality of anonymous SMS in France. The tool is lawful; the use may not be.
Should you hang up before voicemail picks up?
If your aim is to leave no usable trace, yes: hanging up before the beep is the only way to avoid creating a recording. But this reflex has a downside that is easy to underestimate.
A withheld call with no message, repeated, produces the exact opposite of the intended effect. For the recipient, it is the most unsettling scenario: calls with no number, no content, no explanation. In recent news coverage, withheld calls are already overwhelmingly associated with cold calling and scams — several French media outlets reported in early 2026 on the rise in calls with no number displayed and on "ping call" attempts designed to make people call back. Your silent call will be filed in that category, at best; experienced as intimidation, at worst.
There are therefore three coherent attitudes, and one incoherent one:
- Call withheld and speak: you accept that your voice may be recognised.
- Call withheld and hang up before the beep: you leave nothing behind, but you have said nothing either — and you cause worry.
- Write a message: you control the content word for word, and the recipient reads it at their own pace.
- The incoherent one: calling withheld, hesitating, leaving ten seconds of silence with some breathing and background noise. You have created evidence without conveying any information.
For most real-life situations — warning someone, announcing something, asking a question without exposing yourself — the third option wins. A text can be reread before it is sent, which a voice does not allow. Our seven checks before sending an anonymous message apply here word for word, in fact.
Why doesn't #31# work for text messages?
Because SMS does not use the same presentation mechanism as a voice call. A text message necessarily carries a sender address: either a number, or an alphanumeric sender ID assigned to a service. There is no such thing as a "withheld-number SMS" from a consumer mobile: typing #31# before a number in the Messages app has no effect, and may even stop the message from being sent.
This is the most common confusion in this area. To send a written message without revealing your line, you have to go another way:
- a sending gateway that substitutes its own sender;
- a second number (eSIM, dual SIM, dedicated line);
- a messaging app that does not expose your number.
Each of these routes has its limits, its traces and its price. We compared them in our guide to a secondary number with dual SIM or eSIM. And if the idea of borrowing someone else's phone crosses your mind, first read what it means for the owner of the line: writing from someone else's phone does not make you anonymous, it makes a third party identifiable in your place.
How easily can a voice message be kept and passed on?
Very easily, and that is the blind spot of the whole subject. A voicemail is anything but fleeting:
- most carriers offer visual voicemail, which lists messages in an app with date, length and sometimes a transcript;
- a message can be downloaded as an audio file;
- it can be recorded off a loudspeaker by any other device;
- it can be replayed to several people, in front of witnesses.
In other words, your voice becomes a file you no longer control. On the recipient's side, that is precisely what makes it useful evidence: a dated voice message, kept in full, carries more weight than an account of events. For anyone receiving distressing calls, good practice is to not delete the message, note the date and time, and build a consistent file — the method is the same as for building solid evidence from an anonymous message.
And to archive it properly without depending on a carrier platform that purges its messages after a few weeks, a simple digital voice recorder placed next to the loudspeaker remains the easiest method to explain at a front desk: one file, one date, no obscure handling.
What should you do when you receive a withheld call with a voice message?
Three reflexes, in this order.
- Don't call back in a hurry. If the message asks you to call a premium-rate or unknown number, be wary: this is a fraud pattern documented by cybermalveillance.gouv.fr. And if you do have to call back, do it without exposing your own line: we explain how in calling back a withheld number without revealing your own.
- Keep the message. Don't delete it, even if it is unpleasant. It is your strongest piece of evidence.
- Filter without cutting yourself off from the world. Recent iPhones and Android handsets let you route calls from unknown numbers to voicemail, or filter calls with no number, without blocking text messages in the process. The setting and its effects are described in rejecting withheld calls without missing a text.
If the calls keep coming, filing a complaint is the intended route: French criminal law punishes repeated malicious phone calls and harassment, and the procedure is described on service-public.fr. The fact that the number was withheld does not close the case — it simply makes it take longer to investigate.
Withhold your number or write: how to choose?
| Situation | Withheld call | Written message |
|---|---|---|
| Short piece of information to pass on | Risk of voice recognition | Controlled, can be reread |
| Immediate urgency | Relevant if the person picks up | Depends on when they check |
| Sensitive subject, embarrassment | The voice betrays emotion | The tone can be corrected before sending |
| Need for a reply | Impossible: the person cannot call you back | Possible via a dedicated reply number |
| Wanting to leave nothing behind | Only if you hang up before the beep | The message stays, but without your voice |
The last row deserves an honest nuance: neither option erases the traces held by the carrier. A written message does not make you untraceable, it makes you unidentifiable by the recipient. We developed this in our article on how traceable an anonymous SMS really is. The difference lies in what the other person can work out on their own, and in what they keep.
Three practical precautions people often forget
Background noise. If you absolutely must leave a voice message, a neutral environment avoids handing over your context. Noise-cancelling headphones with a microphone isolate the voice and remove some of the clues about where you are — a small detail, but it is often the detail that identifies you.
The recipient's loudspeaker. Assume your message will be listened to in front of someone else. What you wouldn't say to three people, don't say on a voicemail.
Writing allows rereading. Writing an important message on a touchscreen keyboard pushes you towards clumsy brevity. A compact Bluetooth keyboard or a simple notebook to draft in before typing buys you in precision what you lose in spontaneity — and when it comes to anonymity, precision counts.
Finally, if your aim is to stop being contacted or to put an end to messages, the site has a page dedicated to that situation: stop being contacted. And to understand exactly what the recipient sees of a written message, our FAQ pages set out the scenarios carrier by carrier.
Frequently asked questions
Can you leave a voice message without your number showing up? Yes: a call placed with #31# does not display your number, including when it rolls over to voicemail. But the recorded message contains your voice, its date and its length, and the carrier keeps a record of the call.
Can the recipient have a withheld number identified? Not on their own. No app reveals a withheld number. Only a judicial authority can request that data from the carrier, usually after a complaint has been filed.
Does #31# work for text messages? No. A text message necessarily carries a sender address. Typing #31# in front of a number in the Messages app hides nothing and may cause the message to fail.
How long is a voice message kept? That depends on the carrier and the plan: retention ranges from a few days to several weeks on standard voicemail services, while a message downloaded or saved by the recipient has no limit at all.
Is it better to call with your number withheld or send an anonymous message? To pass on precise information without being recognised, a written message is easier to control: it can be reread, it does not carry your voice, and it gives the recipient time to react. A withheld call is only worthwhile if you need to speak in real time.
Updated on 5 November 2026.
