I'm not entirely sure I buy into the theory that technology would be severely retarded in all respects. For one thing, many of the building blocks for today's technology were already in place.
As an example, by 1984, early versions of cellular telephones were in use in a number of places, including the US, the Nordic countries and Japan. With most of the infrastructure for landline service damaged or destroyed, I would expect rapid development and widespread use of cellular technology during the recovery period. It would be far easier to deploy a cellular network than to rebuild the old landline based system. This would not be dissimilar to the rapid growth of cellular in the contemporary OTL developing world.
Along the same lines, the basics of modern computing existed in 1984. The original Apple Macintosh, in fact, was released in January 1984. Given the loss of so many engineers and other technical specialists, I can see the development of computing being given a rather high priority as a means of increasing the productivity of technical specialists for whom the demand will exceed the supply.
Similarly, by the early 1980s, the basic building blocks for the Internet already existed and the Compact Disc was already in use.
So, despite the widespread destruction of the exchange, I would not find it inconceivable for much of today's technology to be in use in an alternate P&S 2012. 28 years is a long time, and even if one assumes that the Exchange set the world back by around 15-20 years technologically, that still puts us somewhere between 1992 and 1997, which would be consistent with a world that takes the rest of the century to stabilize and really begin rebuilding again. For one thing, there's enough left of the United States for it to have its own economic miracle beginning at the turn of the millenium. And that seems to me to be about right -- 16 years to clean up the mess to get to the point where you have a world ready to finally turn the page and look to the future right around Jan 1, 2000.