I usually use for my teleclasses. I have found generally this to be great - and you can also get free recording for MP3 which makes it really useful. I have had a couple of issues on one call with call quality, although generally I have been found.
I also use this service for teleclasses. Once I have more than 20 people, I'm sure I will be looking at some other services. I use dimdim.com for webinars.
I used a few times FreeConferenceCall.com a few years ago, but back then it had few features and the bridge line quality was not always reliable. Now I use www.xiosoft.com ($49.00/mo) which allows me to produce professional quality shows (I can add music at the beginning and end, use sound effects if I chose to, it does a professional recording of my classes, and a few more features). I believe there's a $1.00 trial for a week... or free trial...
I'd definitely say that if someone is at the beginning of their solo-career or are ona tight budget, www.freeconferencecall.com is the way to go. www.xiosoft.com is great once you are generating enough income to easily cover the cost. It's a great service - I'm very happy with it (plus it has an affiliate component, hence, my monthly fee is already covered through my affiliate income)