Hearme make a range of voice communication programs that work over the internet and details can be found at http://www.hearme.com.In the Mudcat context, a Hearme is a group of people getting together for a song circle/ session on an agreed Hearme Voice Creator enaled web page. The one we use is hosted by Aine and can be found at http://www.geocities.com/anneuicocaire/hearme.html. The sessions are usually good fun, can start at any time and are normally announced in a thread here.
The basic requirements for joining in a Hearme session are A PC P100 or higher, running a minimum of win 95 and IE4 or netscape equivilant pluls a sound card and modem. If you meet that spec, the best plan is just to visit Aine's page and see what happens. This will involve a small download of a plugin.
Jon