Internet Telephony
Okay, I've done this enough to think I have a valid opinion. :) Here's what I would recommend, for an Internet Telephony computer. Anything above this, especially a faster Internet connection, like DSL or cable modem, will greatly enhance the call quality and stability.
Operating System: Windows 95, 98, 2000 or NT, with the latest service packs applied. I have not tested any services that support the Mac or Linux operating systems.
Modem Speed: Most services require a minimum 28.8k connection (DSL or Cable Modem is recommended).
Browser: IE 5.01 and above or Netscape 4.5 and above
Computer type: Pentium MMX™ processor or higher is recommended, but not required. Go2Call.com requires an MMX™ processor or higher.
Sound card: Full Duplex highly recommended. Some of the newer 128-bit PCI cards, like the Creative Labs Sound Blaster Live! cards, are beginning to provide hardware support (CODEC) for voice calling.
Other Requirements: headset with microphone suggested, at least a microphone and speakers.
Don't give up on the first IP Telephony Service you try. Some, like www.phonefree.com beat the stuffing out of your processor. Also, the time of day you call and where you are calling will affect your experience. The statistics I've seen show that the net is hit the hardest, between 7:00 PM and 11:00 PM (19:00 and 23:00 hours), their time.
IP Telephony will force you to improve your manners. Even though it is full duplex, it won't be as forgiving as your Plain Old Telephone System (POTS) line. Get used to waiting for the other person to finish speaking, before you speak. Also, upon making the initial connection, if the receiving party says, "Hello," continuously, like a parrot, you may have trouble getting them to hear you, at all. You might be better off calling them on your POTS line or sending them an email, the first time to ask them to say, "Hello" ONE TIME, then pause for a few seconds. Of course, it can also be entertaining to see how long someone will repeatedly regurgitate the word, "Hello," before they begin cursing and hang up. ;)
Here are a few IP Telephony sites: