How can i install Cisco VOIP service in a small firm?

My company is planning to setup cisco voip service to communicate for inter-branch communication. We don't need to connect PSTN phone in voip. please tell me what are the devices that i need to install this service.

regards
nirmal baral

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia��).