Access markets tend, over time, towards relatively-stable oligopolies. The issue is whether, in the internet era, with new platforms and contestants, that can change. Certainly, in the near term--in fact for rather longish periods of time--markets will become unstable when disruptive new technology and new competitors enter a market.
The longer term issue is whether markets--after a period of time--adjust to the altered realities and reform, in stable form, in the form of oligopolies.
In many ways, it is too early to say.
Since the 1980s, when former state-owned telecom networks were privatized, and in the 1990s when new competitors were allowed to enter markets (both mobile and fixed), followed by the advent of the internet as a primary driver of business models and competition, accompanied by shifting end user demand, there literally has not been any respite in the amount of change.
Will there eventually be a period where disruptive change ceases to be such a prominent feature? Almost certainly. Still, for the foreseeable future (perhaps a decade or two), it seems highly unlikely that markets will reform in stable fashion.
There are many reasons for that state of affairs. We have not yet reached the conclusion of a massive change in access provider economics, where businesses driven by supplying voice services, messaging, internet access and video have either made a transition to substitute revenue drivers or consolidated to a point where available revenue and profit level are clearly sustainable for the remaining number of providers.
The larger observation is that we are quite some ways from knowing what stable access provider markets look like, in terms of market structure.