MondialFax

Sending a fax to a mobile

The answer is no — here is why, and what works instead.

You cannot send a fax to a mobile phone number, and no service can: it is not a commercial limitation, it is the protocol. A fax is a voice call during which two modems talk to each other in tones, so the other end has to be a device that picks up and answers in that language. A smartphone picks up and puts a human on the line. On top of that, mobile networks compress voice for the ear, which destroys a modem signal even if a fax machine were wired behind it. MondialFax therefore rejects mobile numbers at input rather than accepting a send that would fail.

What actually happens

The sending fax machine dials a number and waits for one specific answer tone, the one another fax machine emits to say "I am a machine, let us speak T.30". Without that answer the negotiation never starts and the call ends. A mobile does not emit it: it rings, and somebody answers.

Even imagining a fax machine wired to a mobile line, the transport would not follow. Mobile networks compress voice with codecs designed for human speech: they drop what the ear does not catch and reconstruct what is missing. Excellent for a conversation, fatal for a modem signal, which needs the sound reproduced faithfully rather than pleasantly.

It is the same reason a fax fails on a badly configured VoIP line. The difference is that over IP there is an answer — the T.38 protocol, which demodulates then remodulates the signal. On consumer mobile networks that answer is not deployed for ordinary calls.

The three questions people are really asking

"Sending a fax to a mobile" covers three very different needs. Two of them have a solution.

  • "I want to send a fax from my phone"

    That one works perfectly. Your phone is used to pick the document and type the number; the call leaves from our servers, not from your mobile plan. That is exactly what MondialFax does from a mobile browser, free and with no app to install.

  • "My correspondent only has a mobile"

    Then they have no fax, and sending them one makes no sense. The document has to travel another way: email, a message, or a share link. It is the only one of the three where the right answer is to drop the fax.

  • "I want to receive my faxes on my phone"

    Possible, but not over the mobile network: it takes a virtual fax number with a provider, which receives on your behalf and forwards the document by email. You then read it on your phone like any other attachment.

Why the form rejects mobile numbers

MondialFax validates the number before sending and rejects the ranges allocated to mobile telephony in each destination it serves. That rejection is deliberate: accepting the send would give the illusion that something went out, when the call would fail or, worse, ring a stranger's phone with a modem tone on the line.

A rejected number is therefore not a bug. It is the check that stops you believing an important document arrived somewhere when it never left.

Frequently asked questions

Is there any service that can fax a mobile?
No, and a service advertising it is doing something other than what it says: it usually sends a text message containing a link to your document. That is not a fax, it produces no transmission report, and the recipient needs a smartphone and has to tap the link.
What about WhatsApp or a text message?
Those are excellent ways to get a document to someone who only has a mobile — they are simply not faxes. They provide no confirmation issued by the recipient's equipment, which is precisely what you are after when you want a fax.
Can I send a fax from my smartphone?
Yes, with no app and no phone line: open MondialFax in your phone's browser, pick your PDF and type the recipient fax machine's number. The call leaves from our servers.
How do I know whether a number is a mobile?
Every country reserves ranges for mobile telephony — in France, numbers starting 06 and 07. Our form applies those rules for each destination served and tells you before you send; when in doubt about a foreign number, the dialling-code directory gives the expected format.

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