I’ve just had a look at a website that offers Free Conference Call Services. They actually have a whole selection of different services, starting from free and working up to all sorts of extras including the ability to host 350 people and the ability download MP3 versions of your conference. 
So, is it really free? Well, if you go for the no-frills package it certainly is. Each person on the call has to pay their own long-distance charges to participate in the call, but besides that there are no extra charges for the host. If you do a lot of phone conferencing, it’s worth checking out.
I usually only go with the no-frills way. I am technically challenged otherwise. Helps my wallet to be dumb!