Doing that for an open-ended phone number anywhere in the world seems like somebody's full time job to maintain. You'd probably need some database that ties together disparate data sources. Confidence in accuracy probably varies. The best source to use probably also changes.

I feel like somebody googling for a quick code snippet to do that in a single POST request should be aware of how challenging the problem space is. That would be a hint for joe random developer that they've come up with a bad idea and should work on something else. But I probably expect too much.

Are you saying it's routine for cell phone companies to sell live fine location data to the highest bidder? Can I get a source on that? Horrifying if true, enough to make me switch back to landlines.

Back in 2008 I was working with a company in the UK that had an API to do this with O2. It only provided a rough area of where the user was, as it was based on which (single) cell tower the user was connected to.

I'd imagine today MIMO data is good enough to triangulate a very accurate (metres) position.

5G MIMO is sub millimetre 3D accurate to microsecond timing given a good tower time reference.

I've heard anecdotes about this for a while. Here are a few:

https://www.vice.com/en/article/nepxbz/i-gave-a-bounty-hunte...

https://arstechnica.com/tech-policy/2019/01/t-mobile-sprint-...

https://www.theverge.com/2019/2/6/18214667/att-t-mobile-spri...

Here is a Last Week Tonight piece on the topic in addition: https://www.youtube.com/watch?v=wqn3gR1WTcA