"The ISDN standard was first defined in 1988. "

Frequently, I see Statists assert that the Internet was built by the United States Federal Government.  I shut them down with this argument:

Set the "wayback machine" to 1980 or so.  Typically, modems available to consumers were 300 bps acoustic models.  Could you build "The Internet" as we know it today with that?  Absolutely not.  Nor with 1200 bps modems, nor 2400 bps.  9600 bps, which I recall were available in the very late 1980's, would start, although full-motion video would require far more than this.  14,400 and 28,800 bps modems were an improvement.  

So, "The Internet" as we know it could not possibly have come into existence without the bandwidth provided by then-new high-speed modems.  

ISDN would have been very good (initially, it was claimed to be 64,000 bps in early discussion; more later) but by the time it was rolled out in some locations, it was not sufficiently better than then-available modems.  Further, the phone companies expected to be paid relatively large fees for ISDN circuits, as opposed to regular voice channels which were "free" beyond the regular monthly cost.  

Thus, the vast majority of the credit for developing the Internet as we know it, as least before the high-speed dedicated detworks, was to the various companies that figured out how to shove 28,000 bps down a 3,000 Hz voice channel, digitized and companded with mu-law (or a-law) codecs at 8,000 samples per second.

           Jim Bell