From time-to-time I receive "Unknown" caller on my mobile phone. I do not want to answer those calls as I do not trust the identity of a caller. I feel safer if I can see caller name or at least caller phone number.
I do realise that some businesses mask their identity, so they do not receive many return calls from potentially angry customers. However, I don't care.
For emails, we have effective spam-catching filters that often sit on the recipient side. For mobile phone calls there is no effective similar system available (for example registering with a government backed Do-Not-Call web sites, like this one in UK does not help me). I feel a more robust system will block/mute/ ignore/choose-your-action such calls on the receiving end.
Questions: Is there any valid security concern that forces OS vendors to block access to the caller API for the developers? Is there any way to stay safe and secure, but also allow caller API be available for developers (so they can develop legit blocking apps)?