I also don't buy his line that AT&T never threatened to sue anyone over the patent. Maybe not in the strict legal sense of the word, but if my company receives a letter from AT&T's legal department saying "hey maybe you guys should license this technology that you're using, which we have a patent on", then I'm going to pay attention. Why else would anyone give AT&T money after receiving this letter if not for the implied threat of a lawsuit?

Edit: It seems like he has the patent number wrong. US Patent #4555755 appears to be for a multiphase AC control system - http://www.google.com/patents?id=CFg7AAAAEBAJ&dq=4,555,7...