Free conference calling for businesses are not so different than calls among residential or regular consumer customers.
The term "free" is loosely used here. In fact, in this article, it also refers to "free of extra fee" when used within the limit of allowed minutes. For example, using minutes from your cellphone plan may be free of extra charge.
If you own Apple's iPhone, up to 5 callers can be conferenced into one phone call. The only restriction when using cell phone as a conferencing tool is that all parties must be present to continue calling.
Caller #1 connects caller #2, then caller #2 gets conferenced into the call with caller #3. But if caller #1 disconnects during the conversation, the caller #2 also gets disconnected, unable to continue the telephone conversation with caller #3 without the aid of the first person who "bridged" the meeting. In this scenario, the original caller works as the host for the other two.
Callers #4 and #5 can participate with the aid of not the bridger, but those from #2 and #3. Callers #2 and #3 can bring in and add more members to a single telephone call.
Granted this is confusing, and it's easier to dial into a real conferencing service provider instead of trying to save money by holding conversations among five iPhones.
VoIP, Skype etc.
In addition, VoIP or voice over IP service such as Skype also enables conferencing. With Skype though, there is no need for the bridger to prevent from disconnecting. The only restriction is that all parties must be "invited" to each others' Skype friends list before being able to continue conversation.
All these calls mentioned so far can be made free for a small party, but if it becomes necessary to connect to a real, every day telephone line, just Google free conference call service providers to compare duration of allowed calls, participant capacity level and whether or not additional features, such as recording will be needed.