ISDN-PRI is a term used for Primary rate ISDN. It is an ISDN line with 23 DS0 channels. The speed is also very high. 23 DSO is a US standard and 30 DS0 channels is an ISDN E1 which is a European standard and has an even higher speed. ISDN-PRI is a telephone based line and it uses the same for the voice services. So one can use an ISDN line for voice or data transfers. There are many other uses that you can put the ISDN-PRI to use for but all depends on the equipment that is being used during the installation. This also depends on the telephone company's offering. Generally ISDN-PRI is used for telephone voice communication than for data.