TWO LINE Two line sets can access two phone numbers and have no intercom. They usually have a HOLD button. They have only a keypad. The Switchhook is the part of the phone that gives you dial tone when released. Eagle and Extrom sets use a feature or transfer button instead of a switchhook.
Many features require the switchhook to be pressed.
When using the switchhook, press it all the way down, then release it. You will not hang up on your call. Telecommunications will replace these phones with touchtone models at no cost.