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.
There's a few reasons, one is financial - USA wants those installation contracts. Another is that USA wants covert access to those networks (instead of the Chinese).
For me as a private citizen of the UK the Chinese having access seems less likely to impact me than USA having that access.
There's something disturbingly dystopian about governments competing for access to private individual data, and us having to consider which one we're more OK with...
Doesn't explain why the US was equally adamant that western telcos with the know how shouldnt buy "dumb" Huawei equipment, vet it and install it themselves.
This is what made me think that this is at its heart not about security at all and more about just isolating Huawei.
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.