Most operators take a support and maintenance contract. It's also worth remembering that many operators don't have the staff needed to even install radios and other distributed equipment - often the radio vendor can offer that service to you as well.

You can run a mobile network with minimal external access, but the economics are such that few want to - in an era of outsourcing and managed services, it's less about what can be done, and more about what is done in reality.

Managed service providers have significant levels of access into mobile networks, beyond what many are aware.