There are several configurations for landline phones in your home. The configuration that works best for the imp box is when there is one landline phone plugged into the wall, and all other phones communicate wirelessly with the base. The imp is then installed between the wall and the landline base phone so it can filter all calls.
Some homes have more than one landline that plugs into a wall jack. These homes can have their phone lines installed in one of two ways. One way is that one phone line enters the house from the road, and then splits off through the walls to go to the different landlines. This is known as a parallel phone system, and the imp will need to be installed before these lines split, typically at a cable box or junction box, near where the phone line enters the house. This article outlines different options to resolve this issue.
The other type is known as a dual phone line. This is when two or more phone lines enter the house independently. The imp can’t be installed before the lines split. On these systems, the imp can be installed on any phone, but your other phones will always ring once for all incoming calls. The best course of action for resolution is to not answer the phone unless it rings two or more times. You can also get a new phone system where one phone plugs into the wall jack and the other phones communicate wirelessly with the phone base and do not plug into a wall jack.