I use one phone line, but then, I don’t get many faxes. Right now I have to know when the fax is about to be sent to me. The person who is sending it must first talk to me on the phone and tell me he will send me a fax. Then I hang up. When I know the next call is a fax, then, when I see the incoming call on my Windows XP computer, the message reads “Click here to answer this call as a fax call” and I do. However, if I didn’t know when a fax was coming in, this would not work. I would need a separate phone line connected to my computer and I would set my computer to ALWAYS answer the call as a fax call (which can be done). If and when the day comes when I only use my cell phone for voice calls, I WILL use my land line strictly for incoming faxes and set my computer to always answer the call as a fax call. If I had multi-page faxes to send or receive, as well as many voice calls I could not interfere with, then I would also get separate lines. When a fax is coming in to my phone line, I can’t make other voice calls or get incoming voice calls. I DO NOT have an all in one. Faxes come into my computer and when I accept a call as a fax, it goes to my hard drive. If I choose to print it out, it prints on my printer. If you are able to connect your device directly to a phone line (withOUT a computer), you will need to find out from the instruction manual whether or not the device can distinguish fax calls from voice calls. If it CAN, you are in a great situation since the MACHINE will turn on the fax when it needs to but let your phone ring when it’s a voice call.