ISDN allows you to turn one phone line into two, but the magic is that both lines are digital not analog thus enabling you to communicate with up to 64Kbits per line. When coupled with an ISDN adapter and an ISDN service you can surf online with speeds up to 128Kbit which is about 3 times as fast as regular dial up lines. At lower speeds of 64Kbits you can use both the Internet and your phone at the same time.