Windows has a dialler application which was marginally useful for either dialling bulletin boards (in the good old days) or for dialling when modems had pass-through ports for ordinary phones.
To do this with broadband you need a process called VOIP (Voice Over IP). With some, if both pcs have the same software and are on the net, you can connect directly. To call any landline, however, you will need to sign up with a service provider.
If you want to have a try (and save yourself a fortune in normal telephone charges) see this site: click here