> I've yet to read a good explanation of why the telcos permit CLID faking and reinjection of apparently local CLID by overseas inputs.

Actually, there are several legitimate use cases:

• Call divert: Local number calls a number abroad and that one is diverted back a another local number. It's probably rare, but it's a totally legit use case.

• 2G/3G roaming: I'm not an expert on this one, but as far as I understood it, roaming calls placed on 2G/3G networks are initiated in the visiting country, and use the local number of the caller.

• Getting better rates using VoIP. Whether this is legit or not might be subject to discussion, however I was using a foreign VoIP provider (because they had better rates for local calls than any local providers, for my low call volume) sending out my own local number (had to be validated by them by callback, although that's their own security measure, not the network's one). Now in several EU countries and Switzerland this doesn't work any more, as calls bearing national IDs coming from abroad must be displayed as anonymous. And it's quite annoying that there isn't a way to "authentify" those numbers so the owner can use them as they wish.