[est]

So, how do you lookup a phone number's provider for free?

[woodruffw]

Not free for meaningful numbers of requests, but I've used APIs like numverify[1] to do this before. There are probably per-carrier APIs you can request access to.

[1]: https://numverify.com/

[alfredosequeida]

Not the most scientific approach, but you could send a message to every provider using the same number. If you get a "message not received" bounce back, then that's a good indication of which carriers are not the correct carrier.

[AviationAtom]

That was what I came to checkout the code for, thinking they put some cool logic in there.