Voice Over IP for $60, or $200, or $0
 

The idea's simple enough. If you've got a network connection to someone else (a local network, a private Wide Area Network, an Internet connection, or, heck, a dial-up or weirder modem connection), then you can send digitised voice data as easily as anything else. Voice doesn't take up a lot of bandwidth, and it doesn't take a lot of computing power to encode and decode it; any fast 486 or basic Pentium with a sound card, back in 1994, could handle telephony just fine.

http://dansdata.com/skypephones.htm