Recently, I changed a dual-line to an octo-line for one of the users.
After the change, there seems to be an issue with conferencing two existing calls into one.
For example, when he's currently on a call and a second call comes in. He picks up the second call (puts first one on hold) and decides to conference the two existing calls. When he presses the Confrn button, it puts both calls on hold and starts a new call.
On another phone that is using a dual-line, when the user presses Confrn while there are two existing calls, it puts both calls into a conference.