Ah. I think Protege interpreted the question better than I did.
If the question is: "I have DSL and I want to have both a phone line and the DSL line working at the same time, i.e. I want to make phone calls while I am on the internet using the DSL connection," then yes, all you need to do it get a splitter, connect your modem to one side of the splitter and then stick your telephone's connection into a filter (the phone company should have given you a bunch) and plug the filter into the other side of the splitter.
If you want more than one computer using the internet at the same time, you'd need to use the Internet Sharing feature Aptmunich mentioned or the router solution I suggested.
Good luck!