Cell phone service in conflict zones tend to work rather well unless and until a government authority (local or not) knocks it out of service. First off, there is demand for the service because wire-line services of various sorts (including even electricity) tend to be subject to disruption and unauthorized leeching in ways that make the services less reliable and/or more expensive to build and operate than cell phone service.

The cell phone service providers pay baksheesh and/or tower "hosting" fees (sometimes with revenue sharing) because they find that there is money to be made in providing service -- as they can use local "authority" (even say neighborhood gang leaders/warlords to protect an asset that is generating money for the local toughs or traditional leadership (if even differerent) who like their own revenue stream.

Governments -- local and not -- like the services to be there for various reasons -- ranging from support for humanitarian efforts to providing some "legitimate" business opportunities for locals to making for a more extensive and capable surveillance/spying operation than would otherwise be the case.

There is no unwritten rule about not messing with cell towers. [I've seen them become the target of attacks too.] But if you mess with the cell towers, then you infuriate the local population using the service and anger those who make money from the service -- that disruption is not a good approach if you want to try to be operationally in charge on the relative cheap in a specific area or if you like to see money coming your way.

There are payment channels for consumers of cell phone service in conflict zones -- but it's mostly prepaid.

Repairs are done by contractors, some of whom are locals, but some of whom may not be.