Try this......
                                 ISDN
                        -----------!------------
                        |                      |
                     56/64K              Standard Phone
 (Bitsurfr Pro)   Standard Phone               |
                        |                      |
                        ------------------------
                                   |
                             112/128K Bonded
When ISDN comes in your house, it runs just like a normal phone line does..
 (I.E. Two Wires)  From there, it connects to a Terminal Adaptor (TA).
After the TA, You get 2 lines... And depending on what brand you buy, you 
might get a few more added things......
--- Telegard v3.02/mL
---------------