There are many reasons for the use of a phone / network system in your home or commercial setting. Two basic types of systems that can be used in the home are hardwired and wireless systems. Hardwired home systems allow you to send and receive pages, as well as answer incoming calls, answer the doorbell, visually monitor rooms, and open your front gate. Wireless home systems offer many of the same features of a hardwired system with the freedom to be easily relocated throughout your home or office.
Your phone / network system may help in regards to communication inside the house, but it also integrates with your whole home automation system (ie Crestron or Control4). For example, a sensor installed in your driveway, serves the purpose of announcing the arrival to persons to your house. They can call you on the intercom and you would be able to visually see and speak with them preparing you for their arrival. Internally, you can check in on the nursery to make sure the baby is sleeping soundly, let everyone know that dinner is ready, or check on the dog in the yard. Basically a phone / network system is an essential part to your homes automation system overall, allowing you and your family to utilize its features to the fullest.
Commercial businesses with multiple phone lines find managing extensions and separate voicemail boxes a breeze. Internal and external transfers are made simple, and conference calls can be made from several different offices at once.