I would be surprised if this hasn't existed for a few decades already. Back in 2009 I was working at a place where O2 was a client, and they gave us an API tha

I would be surprised if this hasn't existed for a few decades already. Back in 2009 I was working at a place where O2 was a client, and they gave us an API that could identify the cell tower (inc. lat/lng) any of their customers were connected to. The network needs to track this data internally to function, so the API is basically the equivalent of their DNS.