No, you cannot use any modem. As described above, you can’t use a cable modem with a DSL connection, nor a DSL modem with a fiber connection. Your provider typically supplies the correct device for the internet type you have. You can purchase a modem if you want to avoid monthly fees, but it must be authorized by your internet provider. Spectrum, for example, provides a list of compatible modems that work with its three cable internet plans.8 We list the best cable modems for Xfinity, Spectrum, Cox, and more.