The two-line phone works great, as long as only one of my two lines is connected. This goes for both input jacks.
When both of my lines are connected, regardless of which input they are connected to, I get the hum and loss of Caller-ID, etc.
Unfortunately, I do not have any other two-line scenario in which to test this phone. But since it works great with a single line connected, I am assuming the problem is not in the phone.
