Many mobile network operators have committed to become net zero carbon. To succeed, they need to activate many levers, upon which sharing network infrastructures appears as inevitable. In this paper, we highlight some current implementa- tions of network infrastructures sharing. We then compare two different scenarios: a business-as-usual scenario, corresponding to the current situation in France, and a fully cooperative and ideal scenario. Opportunistically using the available data, we draw a model to estimate carbon savings between these two scenarios. This model estimates that carbon savings thanks to radio access network sharing would go up to 79% in France. Indeed, the current French regulation framework, which includes coverage and performance requirements, leads to overlapping networks and high overdimensioning. The savings highlighted in this paper embed the consequences of both. Conversely, the fully cooperative and ideal scenario assumes a change in the regulatory framework, in which network infras- tructures as rather considered as a common good. To favor the emergence of such framework reducing environmental impacts by design, a new indicator, the Sufficiency Deployment Index (SDI), is specified. It measures the sufficiency of multi-operator network infrastructure deployments on a given territory. Future work shall enhance the model, by embracing the consequences of infrastructure sharing, using a consequential approach. Moreover, new business models will have to emerge, created on the economic, social and societal values for all actors of the ecosystem. A single actor cannot change its business model alone.