Older hardwired systems allowed you to take and make phone calls. Most of the time any long-distance phone calls were charged on a rate based on the length of time and call destination. Interoffice communication was done by separate facilities known as intercoms. If you called someone or someone called you where neither or other or one of you were unavailable there were no ways to leave messages. Until the invention and installations of answering machines, the busy signal or endless unanswered ring ended the call. If calls were received by your office on your phone when you were on your phone the caller simply received a busy signal alerting them to the fact that you were on the phone. There was no facility for leaving any type of voice message that would alert you to the fact that the caller had indeed called you and was giving him or her the latitude to leave a message instructing you as to their intentions to receive a call back from you. When you left your office, the phone on your desk became benign. There was no way for a caller to do anything but receive your notification that you were not in the office and to leave a message for you.
Hardware systems have improved. However, they do not equal IP voices systems that have many additional functions that are productive. Many offices today still live with a hardwired system accepting the limitations that hardwire systems available them.
To-date many of the offices that were initially set up using hard-wired telephone systems still use those of system. Many do so out of fear of the cost of a new system and others out of ignorance of the available additional services available with an IP system.