Traditionally PBX systems have used analog copper lines to connect to the telephone network, usually from Bell or Telus. A typical analog business line costs $45-60 per month, and has limited functionality.
SIP Trunks use the existing internet connection to carry voice traffic to StormQlouds high availability data centres, and from there connect to the phone network.
As well as reducing telecom costs by 50-70%, SIP trunks also add functionality. For example, multiple DIDs can share the same SIP trunk enabling direct dial numbers to a particular extension, or for different departments. Customers are also able to set the callerid name and number.