Tracking Down a Harassing Caller Number?

Are there any official procedures or unofficial ways of tracking down the source of repeated harassing calls coming from a set of apparently related numbers in a distant area code?

[Calls may or may not be legally harassing but are certainly unwanted. Callbacks to the Caller ID numbers get a "Your call can not be completed" message followed by a code number. It's most probably some kind of commercial call, rather than a personal harassment.]
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