Some cards like the Sierra Wireless AirCards support the sending and receiving faxes. You need to check out the FAQ for your specific Sierra Wireless AirCard. You will need to specify that the fax will be sent or received using the AirCard. You need software like WinFax Pro and need to configure it to work with the AirCard. You need to check with your ISP to see if they support Fax services (not all do).

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In the case of other cards you will need to check the cards specifications. Most cards should be able to support fax transmission with the appropriate software, like WinFax Pro or others. In some case you might consider a gateway or a fax service where you send e-mail and the service converts it to fax format and transmits if for you.