Teleconferencing is an umbrella term that can refer to many different forms of telecommunication. However, all of them now implement the internet to receive and transmit the audio and visual aspects of a teleconference.
Virtual teleconferencing usually refers to four different specific technologies. These are video conferencing, internet capable telephone, internet collaboration and augmented reality teleconferencing.Additional information can be found at http://countcerlucul.wordpress.com/2013/06/15/video-teleconferencing-codec/. The first two, video conferencing and internet capable telephone, are based on technologies that were introduced to the business world before the introduction of internet access to average consumers in 1996. Internet collaboration and augmented reality teleconferencing are more recent technological developments.
In recent history, the newer virtual teleconferencing technologies have been supplanting the older ones. It's easy to understand why. The newer technologies only require software that can be installed on regular computers. However, older forms of virtual teleconferencing require far more significant investments in hardware designed specifically for the task of teleconferencing. While some older businesses may already have that hardware infrastructure, newer businesses usually simply invest in the newer technologies.