If you have a computer that has no internal modem, or it doesn't work, you plug this into a usb port on your computer and you can connect your telephone cord to it to get online with your Dial-Up service. Anyone who uses dial-up needs a modem. The new computers don't have internal modems like the old ones. They are configured for wireless only. FYI: For anyone who is using dial-up and paying for it, you can save yourself some money, by using "Dial-In Free" . Do a search for it online and get their homepage to get set up. I use it and it works like a charm! I hardly ever have a problem getting online or staying online. They used to be only in Michigan, but a couple yers back they went nationwide! :)