Immediately after graduating from South Georgia Tech, in Americus, Ga. April of 1979, I started with Seaboard Coastline Railroad. Railroads across the country were using antiquated technology. 'Open wire' phone circuits were the mainstay of communications for railroads. We had a very limited amount of Radio selected by coded ring cycles on the open wire Dispatcher circuits. For telephone communications we maintained electro-mechanical 'step plants' made by Automatic Electric and other phone apparatus by Western Electric and Stromberg-Carlson. It was not until the mid to late 80's following Railroad deregulation that Rail technology begin to boom.
In the 80's Amateur Radio was a very active hobby. Some might argue that is still the case. OK, I was never the Ham Radio Operator I should have been. CW was not my strong hold, but I never had a problem moving down the band to 144MHz from my everyday at 161MHz. Over the years I have taken my shot at applying several homebrew solutions to both personal projects as well as work system troubles. Some founded in good science and some found in the Voodoo & the black art of RF and radio electronics....more on that to come!
Thank goodness we have seen significant advancements in telecommunications over the years.
In my opinion reliability is the single most significant advancement. I give pause to the thought of what is the greatest contribution. Maybe progression from analog to digital or the move from discrete components to surface mount components on multi-layer boards. My guess is, it is all of the above along with the lower price of material in the manufacturing of electronics. Consumer electronics is one area in our economy you can spend less and get more as technology advances.