Audio Conferencing Phones are needed when group of people want to use phone at the same time. A typicall phone with speakerphone functionality has ability to deliver far-end audio and able to pick personal voice however it's not enough to be used in a group meeting.
At OfficePlus LLC we have wide variety of conference phones works with Analog telephone line & SIP (open SIP) standard conference phones. They are also available in wired and wireless. Trend of USB audio and Bluetooth is on.