Sending and receiving faxes over a cellular connection is rapidly becoming a 'black art' as more and more MNOs either drop support for "mobile-originate" or "mobile-terminate" fax altogether, or forget to train their customer services staff on the network's fax capabilities.

In order to use your mobile phone, datacard, USB modem (in conjunction with a PC fax application) or embedded cellular fax device (such as the Possio device range http://www.possio.com) to send and receive faxes, you will need to have your SIM card enabled for fax service with the operator. There is usually no cost to have this done, but it is something you will have to specifically request from the operator as it is not enabled by default.

When you are enabled for fax service, you should be assigned an additional telephone number, distinct from that SIM's voice number. It is this number that people who wish to send you a fax should dial: the distinct number lets the receiving device know that it should expect a fax call on that number rather than a regular voice call.

Sending faxes

If you are unable to send faxes, the most common problem is that either you have not been enabled for fax by your operator, or your device simply does not support fax at all.

To verify either of these, the best tool to use on a Windows PC is HyperTerminal, which is included as part of the operating system. Other platforms will most likely have a suitable terminal application - consult the documentation.

HyperTerminal can be launched by running 'hypertrm.exe' from the Run dialogue on the Start Menu.
When running HyperTerminal for the very first time, you may be prompted to enter telephony dialing properties such as your local area code - enter anything, it is not important for our troubleshooting purposes.

Enter a name for the session, 'Test' will do.

You will be prompted to enter a telephone number, enter 0

You will also be prompted to select a connection device from a drop-down menu. Here you should select your cellular data device. If your device is not listed it may be because either that it is not installed correctly (in which case you should resolve that issue first) or that your device is not 'presented' to Windows as a modem, but a network adapter - in which case it will not be compatible with your fax application.

Provided that your device is listed, select it and click Next. On the next screen you will be prompted to Dial. DO NOT click dial, simply click Cancel.

You will now be presented with a blank screen with a flashing cursor - you have established a terminal session with your modem.

Verify that you can communicate with your modem by typing in:

AT (enter)

You should hopefully receive an 'OK' response.

Now verify that you are indeed 'talking' to the correct device by typing in:

ATI (enter)

You should receive details of the device including manufacturer and model number. If you receive details of the PC's other modem devices then you inadvertently selected the wrong device earlier, you should close HyperTerminal and start again.

Provided that you are indeed talking to the cellular device, verify that the device is registered on the mobile network and has a decent signal strength:

AT+COPS? (enter)

Should return the name or 5-digit "SID" of the network operator.

To verify that your device supports fax at all, type in:

AT+FCLASS? (enter)

You should hopefully see something along the lines of:

+FCLASS=0,1,2,2.0

Which indicates that your device does indeed support fax. If you see only:

+FCLASS=0

Then that would indicate that your device is not fax-capable.

Provided that your device is fax-capable, set the device to fax mode by entering:

AT+FCLASS=2 (enter)

Now try dialling another fax device by entering:

ATDxxxxxxxx (enter) 

where xxxxxxx is the number to be dialled.

If your device immediately returns a response of

"NO CARRIER"

then your SIM card is not fax-enabled by the operator.

If you see a response from the receiving fax machine (which will consist of the name and number of the answering machine) then you have successfully established a fax connection.

Should the above troubleshooting indicate that your device is fax capable, but you cannot send faxes from within your fax application, verify that the number entered is correct (and that the fax application is not adding any area code or other dialling digits itself) and also that the fax application is configured to use the correct modem device rather than an internal device.

Receiving Faxes

Receiving faxes is a lot more complicated than sending faxes over a cellular connection. Even if you have no intention of sending a fax from your device, but only want to receive faxes, when troubleshooting fax reception issues, you should always verify that you can send faxes first using the above troubleshooting procedure as any failures will indicate where the problem lies clearer than troubleshooting the other way around.

Provided that you can send faxes successfully, you are enabled for fax. Receiving faxes requires that your SIM card be assigned an incoming fax number, distinct from the voice number, as mentioned above.
When troubleshooting fax reception, you should first ring the fax number and make sure that it is in service. You should also try ringing the number when your device is not powered on: if the call is still answered and you hear fax tones, then the network operator has assigned you a "fax mailbox" rather than a direct incoming fax line to your SIM.
Provided that your device appears to be fax-enabled, but when dialling the number your device rings but the fax application never answers the call, ensure that the fax application iss et to 'auto-answer' and that it is set to monitor the correct modem device for incoming faxes - this is often configured separately from the sending options.

If you do not have a fax application, but you wish to verify that your SIM and device can receive faxes, you can use HyperTerminal. HyperTerminal will not receive the fax as it is merely a terminal application, but it will answer the call and prove the functionality.

Start a HyperTerminal session to your device using the instructions above.

Once connected, set the device to fax mode with the command:

AT+FCLASS=2 (enter) 

Now set the device to wait for an incoming call answr after 2 rings with the command:

ATS0=2 (enter) 

Now try sending your device a fax on its incoming fax number.

Hopefully you should see HyperTerminal answer the call and display the information of the sending fax device.
If HyperTerminal does not answer the call, but does indicate that a call is incoming (by displaying "RING" on the screen), then that would indicate that the device is not recognising the call as a fax call, which might indicate that the mobile operator has not assigned a fax line, but rather either an additional voice line or a data line. This should be addressed with the mobile operator.

Configuring Windows XP Fax software

Open the Control Panel and double click on the icon for Printers and Faxes

If Faxing has not been previously configured you will see an option to Set up Faxing on the top left hand corner of the screen. You may be prompted for the Windows XP CD to install the necessary software.

If faxing has been configured you will see a Fax printer listed:

To configure faxing, right click on the icon for the Fax printer and select Properties

Click on the Devices tab

A list of installed modems will be displayed.

The fax software does not allow much configuration. Modems can either be enabled or disabled to send or receive faxes.

To configure a device highlight the appropriate modem and click on Properties

To enable sending on a device tick the option to Enable device to send

To enable receiving on a device click on the Receive tab and tick the option to Enable device to receive

You will have the option to receive faxes manually, or automatically after x amount of rings.

Click OK

To enable automatic reception of faxes click on the Tracking tab

Ensure that monitoring is enabled on the correct modem

Note – if monitoring is enabled, this may render the modem unusable by other applications.