That is correct. It is a single base unit with multiple handsets. They can add more lines to it as "Other Phone" type which in essence gives it a 2nd / 3rd / 4th DL. Those DLs can then be assigned to other extensions if they wish. They can also assign which handsets should ring on incoming calls for each individual line. They can ring both handsets or just one of them. All that is done in the GUI of the base unit.If you need help with this, you'll probably want to give us a call.