Pagoo

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

Net2Phone

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

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

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/