VOIP- ( http://en.wikipedia.org/wiki/Voice_over_IP) Voice over Internet Protocol, also called VoIP, IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of voice conversations over the Internet or through any other IP-based network.
A broadband hard phone is a self contained IP telephone that looks just like a conventional phone but instead of a conventional phone jack, it has an Ethernet port through which it communicates directly with a VoIP server, VoIP gateway or another VoIP phone. Since a broadband hard phone communicates directly with a VoIP server, VoIP gateway or another VoIP phone it does not require any personal computer nor any software running on a personal computer to make or receive VoIP phone calls. It can be used independently, all that is required is an internet connection.
A soft phone is an IP telephone in software. It can be installed on a personal computer and function as an IP phone. Soft phones require appropriate audio hardware to be present on the personal computer they run. This can either be a sound card with speakers or earphones and a microphone, or, alternatively a USB phone set. Soft phones are inferior to hard phones but cheaper to obtain, many are available as a free download.

VOIP is also possible to use with mobile phone with significant reduced prices for connections.
What are you thinking about implementation such a possibility as a way of economizing company phone rates?