This book starts out way in the past, from a time of around 150 years in the past. The telegraph had been invented and people were starting to figure out how to use the telegraph to communicate between continents separated by vast oceans. The only way that this seemed possible was to lay long cables on the ocean floor. There were people who were ready to volunteer lots of time and effort in order to try and execute these contracts. However, laying cables on the ocean floor is not easy. You need to have an idea of the terrain underwater, to figure out how to repair if things went bad. In addition, there was another practical difficulty in finding ships that could carry these huge quantities of heavy cables. But this was the start of modern communications.
The book then moves onto the development of telephony, about using the ionosphere to bounce off radio waves, and the steps involved in the development of the radio. Then the book moves onto the idea for which Clarke is famous; the placing of satellites in geosynchronous orbit so that they always seem overhead, and which forms the basis for modern communications.
The last part of the book talks about his predictions for the future. Given that this book was written in 1992, it is good to check about what are the things that came true, and the things that he missed.
The best part of the book is that it does not read like a dreary telling of history, but is written in a gripping way, and keeps interests alive.