A method and apparatus for implementing a presence based universal camp-on feature in packet-based telephony systems are disclosed. A first packet-based device is subscribed to a line status of a second packet-based device. A first notification is received into the first packet-based device from the second packet-based device when the line status of the second packet-based device is in a busy state. A second notification is received into the first packet-based device from the second packet-based device when the line status of the second packet-based device is in an idle state. A user of the first packet-based device is prompted with an option to establish a communication session with the second packet-based device upon receiving the second notification into the first packet-based device. A communication session is established between the first packet-based device and the second packet-based device in response to receiving an accept-call command into the first packet-based device. The first packet-based device and the second packet-based device may be packet-based telephones, such as Session Initiation Protocol (SIP) telephones.