One of the primary tools used by regulators to introduce competition in telecommunications markets has been to impose interconnection requirements on dominant carriers.
This began to change in the landmark case Hush-A-Phone v. United States [1956], which allowed some non-Bell owned equipment to be connected to the network, and was followed by a number of other cases, regulatory decisions, and legislation that led to the transformation of the American long distance telephone industry from a monopoly to a competitive business.
This further changed in FCC's Carterfone decision in 1968, which required the Bell System companies to permit interconnection by radio-telephone operators.
As an example of the use of commercial arrangements, the focus by the EU has been on "encouraging" incumbents to offer bundles of network features that will enable competitors to provide services that compete directly with the incumbent.
Further the interconnect regime decided upon by the regulator has a major impact on the development/rate of growth of market segments.