This article, the fifth in a series on the history of packet switching, provides an account of the early days of commercial packet switching services in the United States. It is remarkable and refreshing - and possibly controversial - in stressing the business of technology more than the technology itself. The previous articles covered the early history of packet switching in the UK (by Peter Kirstein, February 2009) and in Canada (by Tony Rybczynski, December 2009), the early history of the Internet (by Len Kleinrock, August, 2010), and the development of X.25 virtual circuit networking in France (by Remi Deprés, November 2010). Commercial packet switching networks were launched in most countries by the Postal Telephone & Telegraph administrations (PTTs), but the situation in the U.S. was different. AT&T was the dominant communications service provider, but initially showed little interest in packet communications. Entrepreneurial companies, particularly Telenet and Tymnet, became leaders in commercializing packet switching services. The earlier articles in this series described the technical history of packet switching and the development of the international X.25 standards. This article focuses on commercial, competitive and regulatory developments in the U.S. and is written by key figures in these developments. Larry Roberts is generally considered one of the pioneering architects of packet technology and, in particular, the ARPANET, and was co-founder and President of Telenet, the first regulated commercial packet carrier in the world. Stu Mathison was VP of Planning at Telenet from its creation until it became a part of Sprint in the 1980's. Phil Walker, an attorney, was also a co-founder and managed Telenet's regulatory and legal affairs.