I have just learned that my modem was not installed properly. It should have been connected to our main box which connects to the home jacks for phone/fax, tv etc. My security company discovered this as they were trying to connect us. Since May our fax machine is not working properly. I'm told all telephone and data jacks are supposed to run through the panel to the modem. I believe this could be the problem with the fax number. We can send but not receive. Now I know - but a word to new modem users to have it done properly at their homes.