(1) Use modem, you need a modem with "duplex function", i.e. speaker modem or something like this. If you have this kind of modem, software should come with it. But, you will use phone line.
(2) Easy and cheaper way. Use you BB and install Skype, use Skype out function to call any landline in the world (very cheap) click here. If other person is on PC, then install PC on his PC and you can call them via Skype free. Skepe is THE best VoIP program available now.