If you reside in the UK, I've got another great site for you!! http://www.conferencenow.co.uk/ is a Free Conference Call site where you can make international or local conference calls for only the cost of a regular phone call!
All you have to do is dial in with your designated pin, have your contacts dial in with your designated pin, and you're all set. Not only that, but you can even set it up in email calendars such as Microsoft Outlook!
The site is run by MeetingZone Group, which is the largest independent conference call provider in the UK. During the call, you have access to several great features such as muting, locking, and getting an attendee count. There are different dial-in numbers for international calls, and you never have to set up a contract - it all goes through your standard telephone bill!
All in all, this site offers a very comprehensive site for any business who needs to make infrequent conference calls and doesn't want to have to pay a monthly contract rate. It's a very great free conference call site!