I am a happy Windows 98SE user, but no one seems to do internet telephony except for XP -- or have I missed a trick? CPCP
Most of the old instant messaging programs do VoIP (Voice over Internet Protocol) between IM users, and most can do it with Windows 98/SE, as well as XP. Examples include Yahoo Messenger with Voice, MSN Messenger, and AOL's AIM and ICQ. These also let you share photos and add a webcam for video chat. The drawback is that usually you can only talk to people on the same messaging service. New VoIP programs such as Skype and Google Talk require Windows 2000 or XP, but Vonage, for example, works with "Windows 98 SE & above". Skype also works with Mac OS X, Linux and Windows CE.
Update: Skype may work on Windows 98/SE/Me but Skype says: "Because it hasn't been fully tested, we have not yet certified Skype for use with these operating systems."