In short. To text a client without handing over your personal number, four channels exist: a secondary number (eSIM or app), an alphanumeric sender ID through an SMS gateway, an online sending service with a service number, or a messaging app under a professional profile. Be careful: as soon as a message has a commercial purpose, French law requires an opt-out mechanism and prohibits complete anonymity of the sender.
Information verified on 23 October 2026 on the public pages of Arcep, the CNIL, service-public.fr, Légifrance, the 33700 scheme (AF2M) and on the public support pages of Apple, Google and French mobile operators. This article provides general information and does not replace the advice of a legal professional.
Why a personal number given to a client never comes back
Because a mobile number has become an identification key, not just a contact detail. Once handed over, it circulates: address books, the customer record in an invoicing app, a WhatsApp group for a building site, a screenshot sent to a neighbour "looking for someone reliable". You no longer control either its spread or how long it is kept.
The problem is very concrete for three groups:
- freelancers and tradespeople who work from their personal phone, with no dedicated line;
- occasional sellers (holiday lets, private tutoring, small jobs) who have no business structure and no desire to set one up;
- employees who need to warn a client about a delay outside office hours, without access to work tools.
In all three cases, the reflex is the same: you open the Messages app and type. The message goes out, and with it an identifier that will follow you for ten years. We have explained elsewhere why a phone number now works as a quasi-national identifier: it serves as a login, an account recovery key, and a joining point between files that should never have spoken to one another.
The point is not to hide from a client. It is to avoid giving them the same line used by your bank, your doctor and your family.
What is the difference between "anonymous" and "separate" in a professional context?
A decisive difference, and this is where most people go wrong. Anonymity means the recipient cannot know who is writing. Separation means they know perfectly well who is writing — you, the plumber, the owner of the holiday cottage — but through a different channel than your private line.
In client relationships, it is almost always separation you should aim for, not anonymity:
| Objective | What the client sees | Suitable solution |
|---|---|---|
| They know who is writing, but not my private number | A secondary number or a sender name | Secondary number, alphanumeric sender ID |
| They must not be able to call me back at all | A service number or a no-reply sender | Online SMS gateway |
| They can reply, but not to my line | A separate return number | Secondary number, web inbox |
| They must not know it is me | Nothing identifiable | Rarely legitimate in a commercial context |
The last row deserves a warning. A message with a commercial purpose sent with no identification of the sender puts you outside the rules applying to direct marketing (see below). Strict anonymity remains justified in other situations — reporting wrongdoing, a delicate first approach — but not for selling a service.
How do you get a second number without changing phones?
With an eSIM, which can be activated in a few minutes on most phones sold since 2020, or with a second physical SIM card if your device has two slots. You keep a single device, two lines, and you choose which one sends each message.
Steps to check and activate:
- Check compatibility. On iPhone: Settings → General → About, look for the "eSIM" or "eSIM IMEI" line. On Android: Settings → Connections → SIM manager (Samsung) or Settings → Network & internet → SIMs (Pixel).
- Take out a second line with a French operator (Orange, SFR, Bouygues Telecom and Free Mobile all offer eSIM on their mobile plans), or keep a very low-cost plan dedicated to your business.
- Name the lines ("Personal" / "Work") to avoid sending from the wrong one.
- Set the default line for SMS: on iPhone, Settings → Messages → Send from; on Android, the preferred SIM for SMS menu.
- Test it by texting yourself from the work line to the personal line.
If your device does not support eSIM, an entry-level unlocked dual-SIM phone reserved for professional use does the same job, with the added advantage that you can switch it off on Sundays. It is often the healthiest choice: the boundary becomes physical, not just software-based.
We devoted an entire article to the subject, with the exact limits of the method, in our guide to secondary numbers using dual SIM and eSIM. The key point to remember: this second line is registered in your name. It protects your private number, not your identity.
What is an alphanumeric sender ID, and who can use one?
It is a name displayed instead of a number — for example "WORKSHOP" or "DUPONT-PLUMB" — transmitted through a professional SMS gateway. The client sees the name in their message thread, no number appears, and they cannot reply: the "Reply" field is disabled.
Things to know before committing to it:
- an alphanumeric sender ID is requested from an SMS provider, who verifies the identity of the principal placing the order;
- it is one-way: no reply is possible, so it is unsuitable for a conversation;
- in France, industry rules govern the labelling of commercial messages and require an opt-out notice for direct marketing;
- most providers charge per message, with a minimum purchase.
The technical workings are the same as those described in our article on the real identity behind the sender of an anonymous SMS: your number is not hidden, it is absent from the message. Hence the impossibility of replying.
This channel is perfect for appointment reminders and confirmations: "Your appointment is confirmed for Tuesday at 10am." It is entirely unsuitable for a negotiation, a request for clarification or exchanging photos from a job site.
What if the client needs to be able to reply?
Then you need a separate return channel, set up before you send. That is the fundamental rule: a reply always goes to the sender address written into the message, never anywhere else. If that address is absent, no reply is possible.
Three setups work:
- Secondary number (eSIM, second-number app): a normal two-way conversation, on a number that is not yours.
- Web inbox offered by some sending services: the client's reply arrives on a web page, not on a phone.
- Encrypted messaging under a professional profile: the client sees a pseudonym or a trading name, not necessarily your number — provided you configure the profile's privacy settings correctly.
The full breakdown of the four possible return channels, with their limits, is in our dedicated article: receiving a reply to an anonymous message without giving out your number.
One common mistake deserves naming: writing "reply here" in a message sent from an alphanumeric sender ID. The client tries, fails, concludes it is a scam, and you lose the job. Always state which channel you want to be reached on, and check that the channel actually exists.
What does French law say when the message is commercial?
It distinguishes two regimes, and confusing them is costly. An administrative message (appointment confirmation, delay, tracking an order in progress) falls under performance of the contract. A direct marketing message — offering a deal, following up with a prospect who asked for nothing — falls under the rules on cold outreach.
For SMS marketing addressed to private individuals, the CNIL points out in its file on commercial prospecting that the principle is the person's prior consent, and that every message must include a simple, free way to object to further solicitations. In practice, this takes the form of a "STOP" notice followed by the appropriate number or code — a scheme managed in France by AF2M, which also operates 33700, the reporting service for unwanted texts and calls.
Two direct consequences:
- a commercial message cannot be completely anonymous: it must allow the sender to be identified and the right to object to be exercised;
- technical anonymity (an alphanumeric sender ID) is compatible with the law provided that the sender is identifiable and the STOP mechanism is operational.
A third point, recent and often overlooked: French regulations on telephone marketing have evolved, with tighter rules on the display of numbers used to call and prospect. The exact conditions are detailed on service-public.fr; the spirit of the text is clear — it aims to prevent professionals from calling from a non-attributable number. In other words: on the professional side, the trend is towards more identification, not less.
We covered the general framework for anonymous sending in is it legal to send an anonymous SMS in France. The rule fits in one sentence: anonymity is not an offence, but it erases none of the obligations that apply to the content of the message.
How to organise the separation day to day without wearing yourself out
By deciding once and for all what goes where, then sticking to it. The most elegant setups fail on a detail of convenience: after two weeks, you reply from the wrong line because it was quicker.
A few habits that last:
- One address book per use. Professional contacts in a dedicated account, not mixed with personal ones, to avoid cross-syncing to services you never chose.
- One number displayed everywhere, and only one. On quotes, your email signature, the van, your online listing: always the work number. A private number that appears just once on a public document is a public number.
- Organised silence. A Focus mode (iPhone) or Priority mode (Android) configured to mute the work line in the evening: that is also what separation is for.
- A written record of important exchanges. A job-site logbook or a simple paper diary is enough to note the date and subject of a call: useful if a dispute arises, and independent of any device.
- An offline backup. An encrypted USB stick holding quotes and confirmations saves you from having to dig months of conversations out of a phone you will eventually replace.
If an exchange turns sour — insults, threats, repeated pressure — preserving the messages becomes a legal matter in its own right. The method for building a usable case file is described in our guide on the evidential value of a text message and how to preserve it properly. And if the harassment comes from a withheld number, reporting goes through 33700 and, depending on the severity, through filing a complaint: no private procedure can identify a sender, only a judicial request can.
What the client sees, depending on the channel
| Channel | What is displayed | Reply possible | Identity revealed |
|---|---|---|---|
| Personal line | Your real number | Yes | Complete |
| Second number (eSIM / app) | A number unknown to them | Yes | Name held by the operator |
| Alphanumeric sender ID | A name (e.g. "WORKSHOP") | No | Principal known to the provider |
| Online sending service | Service number | Depends on the service | Provider's logs |
| Encrypted messaging | Pseudonym or trading name | Yes | Varies with how you signed up |
None of these solutions is "untraceable". In every case, an operator or a provider keeps technical logs that can be disclosed at the request of a judicial authority. That is the point we developed in is an anonymous SMS really untraceable, and it holds just as true in a professional context: discretion towards a client is not opacity towards the courts.
To compare the options methodically before committing, the site's comparison of sending solutions and use cases pages run through each scenario with its recommended channel.
Frequently asked questions
Can I hide my number with #31# for a work text message?
No. The #31# prefix only affects how your number is presented on a voice call. An SMS travels with its sender address in the header, and no code dialled on the keypad removes it. Typing #31# before a number ahead of a text hides nothing.
Am I allowed to text a client from a number they do not know?
Yes, nothing obliges you to use your personal line. However, if the message has a commercial purpose, you must remain identifiable and offer a way to opt out, in line with the rules set out by the CNIL on direct marketing.
Is a second-number app enough for professional use?
Often yes for modest volumes, provided you check two things: that the number supplied is a French mobile number (some are foreign, which makes clients uneasy) and that the subscription is never interrupted, since a surrendered number can be reassigned to a stranger.
How do I stop my work number ending up in marketing databases?
By reserving it for strictly necessary documents and registering it on the do-not-call opt-out schemes. A number published in an online listing is scraped very quickly: prefer a contact form where possible.
What should I do if a client becomes so insistent that it amounts to harassment?
Keep the messages unaltered, note the dates, and report abusive sending to 33700. Depending on the severity, filing a complaint allows proceedings to be opened; harassment by electronic means is punishable under the Criminal Code, whatever number is used.
Updated on 23 October 2026.
