It’s not only Three issue. Giffgaff has just the same problem. I note that the same problem does not exist with other branded handsets on those networks.
I now have moed to Vodafone. Vodafone and Fairphone 3+ are compatible and caller id works fine. It would be really useful if we compiled a list of compatible pairings. Do we have the same problems with FF4 and FF5?
Nick