Why don't I need a separate fax number to send fax calls over GSM?

When you send a fax call over the mobile phone network, the device that is sending the fax eg. Cellfax Plus, will tell the network that it is a fax call. The mobile phone network can then route the call to an appropriate modem on their network that is capable of delivering the fax transmission to the PSTN Network.

Why do I need extra numbers to receive fax calls over GSM?

If you want to receive fax calls via GSM, you must get and use the incoming numbers provided by your GSM network provider. You will therefore have separate incoming numbers for Voice (your current mobile phone number) and Fax at 9,600 baud.

Someone sending you a fax will need to send the fax to this dedicated fax number. This will allow the mobile phone network operator to receive the call onto its network using a suitable modem that can deliver the fax transmission correctly across its mobile network.

If you attempt to send a fax to the normal voice telephone number, the call will enter the mobile phone network on a standard voice connection, which will be unable to provide the correct transmission protocols and the fax transmission will fail.

Some networks (O2, Vodafone) will provide separate telephone numbers for incoming voice and fax calls so that the faxes sent to the fax number can enter the mobile operators network on the correct equipment, and other networks (Orange) will use the same number as the mobile phone number, but route all calls via a fax enabled service so that both voice and fax calls will work on a single number. However this may change as operators update their services.

At present faxing over 3G (3 mobile) is not supported which is why there are no 3G Fax Modems available.

How can I get my mobile phone company to understand what I mean by the term "Fax number"?.

Most mobile phone companies offer fax services whereby they will issue you with a fax number and when a fax is sent to that number they will send an SMS notification to your mobile phone and you will then need to go to a fax machine and dial the number they give to download your fax. Alternatively they may offer a fax to e-mail service.

if you are using a GSM Fax terminal like the Cellfax Plus then these are not the services you require. You can explain to your mobile operator that you will have a fax machine connected to thier network using GSM fax terminal and that they should activate or set up fax services on your account as detailed above for inbound faxes. if the person in customer services is unable to help then you can speak to somebody about mobile data services (not mobile internet) and as a last ditch give them information about the Nokia Communicator (a mobile phone that is no longer manufactured, but was able to receive faxes directly to the phone and which also needed a seperate fax number in order to do so) and this might help you get to speak to the correct person who understands your requirement.