I once had an idea for an app for managing multiple phone numbers.

The idea being you would have a unique phone number or ext for each contact you want to give. Don't know if it's viable or not.

But I think there's need to be a unique key for everyone you give your number too.

This would enable two things.

1. Discard it as soon as it has been compromised.

2. Know who is leaking your information.

I don't really know if it's a viable solution to implement in practice though.