In this sector the title says it all. It is everything that has to do with communications: phones, cellular phones, cellular equipment, software for phones, and the infrastructure to move signals. The sector exploded right along with technology in the late 1990s as the internet brought the two sectors together. They have since separated again and telecom has a force driving in more business (expansion of cellular) and one driving down business (landlines, long distance).
Almost all the major world players are at least partially owned by their respective governments except for AT+T and Verizon in the US. Other majors are Vodafone, France Telecom, Telefonica and China Mobile.