Phone recording to PC

[Luthien]

What is the simplest way to record phone calls on my phone line which is a digital phone line via sunrocket (meaning it uses my cable modem) to my pc? I have an rjll (phone jack) to mono 2.5mm jack and an adapter that converts that into 3.5mm stereo jact that I can plug into my sound cards mic port but the software I am using doesnt detect anything. Also when I connect it kills the other lines in the house in affect requiring me to use the one phone line that has the setup only. Before I go out and buy something else to play with I would like some input from those that are already recording their phone calls to their pc.