Your Brother MFC7830N should be hooked up using an ehternet cable.
Your cost for receiving & sending unlimited faxes will be the cost of your telephone line.
You need to assign a static IP address for your MFC machine.
You then install the MFC on each client computer as a NETWORK PRINTER.
Here is the instruction manual for yuor MFC printer
http://www.brother-usa.com/ModelDoc...20Manual/NUM_MFC_7225N_7820N_EN_1277.PDF
Hope this helps
Grenville