ISDN stands for Integrated Services Digital Network. It is a digital phone line that allows you to send and receive voice, data, images and video conferencing over the one line.ISDN Fractional Rate Access (FRA) is the ideal solution for growing companies and includes 16 individual channels that can carry voice or data. Additional channels can be added as your business grows. ISDN Primary Rate Access (PRA) is ideal for larger businesses providing 30 channels each capable of carrying voice or data.