After I posted the above message, Rupa Schomaker sent me a list of over a thousand NPA-N00 combinations. I certainly didn't realize there were that many! I have posted Rupa's list atIn a later message, danny burstein suggested:
Neither Rupa nor I had considered toll-free numbers. If we include toll-frees, an obvious one is 800-800-8000, the Super 8 Motel Reservation Line.
Super 8 started using that number before 888 numbers existed. A few years later another obvious choice would have been 888-888-8888.