The PBX is connected to the local telephone company by a common group of lines called PBX trunk lines . An Attendant Console is also known as a Switchboard . PSTN stands for Public Switched Telephone Network which simply refers to the local, long distance and international phone system that we use every day. Your customers and colleagues who are not on your local PBX can call directly to your direct number without going through the attendant console. In order to allow this, the phone company must specially configure your trunk lines.
Capital costs can be significant.
There is an additional charge for DID features. The telephone company will also charge your department to reserve you and your colleague's block of direct numbers. The lines are charged at a significantly higher rate than standard business lines. The system will also need to be maintained. Your department may pay those charges annually or the maintenance charges may be included on your monthly telephone bill.