This is a silly question.
> 1. What kind of software/hardware is used for those
> phone-chat/party-lines?
Try searching for audio conferencing bridge and you might get to TEC or Aastra or any number of companies that manufacture this equipment. At the bottom end, TEC makes a 9-port unit for about $600. A good Aastra will cost 10 times that for 24 ports and you still have to get the lines into it. The Aastra will handle VOIP/SIP connections. Somewhere in-between you can find a 16-24 port unit for about $3K.
2. How would I go about setting up a server that can work as an online
> answering service?
Online to what? I have an auto attendant and personal extension online to my Packet8 line at 567-202-4152x200. I also have a voice mail to e-mail account that costs me $15 a year
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It isn't much different than an answering machine. You could duplicate this with almost any IVR system or roll your own with a Asterisk PBX.
Since the hardware isn't cheap, you're going to have to have somebody WANT to use your service, but that's your business plan, not mine :-) Carl Navarro