Even when having an ISDN phone connection at home you will be able to send a fax. There is no analog connection needed. The only requirement is an installed Fritz!Box Fon from AVM which acts as your telephone system. Via its configuration web interface you can already specify a number to receive faxes. But also sending a fax is possible in some simple steps.
Download and install Fritz!Fax on your Windows machine. A printer driver is installed automatically which is used to send b/w or colored faxes. Works like a charm.
Thanks AVM even it is an unsupported software.