Here are some paid conference call options that you might consider for situations in which freeconferencecall.com or Skype will not suffice. We have found that quality sometimes degrades when more than approximately 10 people are on a freeconferencecall.com call.
ReadyTalk (http://www.readytalk.com/) accounts allow for instant conference calls (no reservations required). ReadyTalk also provides web conferencing services.
You can set up an account directly with Ready Talk or can do so through a re-seller. Re-sellers tend to be more expensive than purchasing directly from ReadyTalk.
UC Berkeley has an account with a discounted rate. Perhaps other partner institutions has the same or could negotiate something similar.
ReadyTalk's standard rate for audio conferences is $0.10 per minute per participant. See pricing page .
ConferenceCall.com (http://www.conferencecall.com/index.php) re-sells ReadyTalk and is matching their standard call price, but as of Dec 31, 2010 that price is presented as a temporary discount.
SoundConnect Now (http://www.soundconnectnow.com/) is a full service provider. They can offer prices as low as $0.035/minute.