Simply put.....

It s the second channel of a special feature added to station ports on the main board of the iDCS systems. By Adding a KDb card to any 18 or 28 button iDCS telephone, you can create a whole nother extension, different than that of the mother station. You can choose from another Digital Phone, or a Single Line Phone. Note: This feature cannot be used on 16 DLi cards, only 8 DLi cards.