Caller ID Question

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I know Caller ID for the common man didn't go through here in Cal.,
despite the fact we have call return.
I have a friend in politics who'd like caller ID to screen out 'junk' calls.
Is it possible to implement it, and if so, where would any hardware mods
be necessary (or is it strictly a Pac.Bell switching thing).
[He wants to know if there a way, legal or not, to do so strictly from his
end].

Thanks in advance ...

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