in hackers the punk using the phone box spliced into the phone line and connected his modem to that, Its been a while since ive seen it, and ive never properly watched it but he might of been using an acoustic coupler..basically if you imagine picking up your phone when your on dial up and holding it to another phone then it uses that other phone. acoustic couplers were used in the begining on the net, you see one used in wargames also where he places the phone in a holder.

he could also of been blueboxing to get the free call.

i2c