Pagoo  
   Answer calls and make long distance phone calls while online.
   http://www.pagoo.com/

VocalTec  
   Enables voice and multimedia communications over packetized networks, the Internet and intranets.
   http://www.vocaltec.com/

PC-Telephone  
   Make free pc-to-pc and cheap pc-to-phone and pc-to-fax calls over the Internet and ISDN/PSTN telephone networks. Use your computer as internet telephone, ISDN phone, answer phone, caller id, fax software and voicemail client.
   http://www.pc-telephone.com

PalTalk.com  
   Enables live video calls, conference calls and voice chat-rooms.
   http://www.paltalk.com/

Net2Phone  
   Voice calls from your PC to any phone.
   http://www.net2phone.com

BuddyTalk by InnoMedia  
   A 4-in-1 Internet voice communication tool for staying in touch with associates while online. Provides downloads of free software.
   http://www.buddytalk.com

DialPad.com  
   Make long-distance phone calls with your PC.
   http://www.DialPad.com

Callwave  
   Internet Answering Machine software uses Busy Call Forwarding to answer and record callers messages while you are on-line.
   http://www.callwave.com/

Internet Call Manager  
   An easy and inexpensive way to stay on-line as long as you want and never miss a phone call.
   http://www.internetcallmanager.com/