Which might be required sooner than one would otherwise expect, if they are threatening to execute warranted searches (BTW this translates to a need for dynamic entry, or worse, in the minds of some ATF, cf. Waco, Ruby Ridge, etc.). Once they have one on a minor charge, they can use it as leverage to bargain away omes' other rights.
Still, an automated screening would seem to be a good idea under the circumstances. I would imagine the feds would be loath to identify themselves and make threats that are obviously being recorded. If it's a friend, of course one can always just pick it up.
Another embellishment of this idea is that once picking up the FBI call, simply inform the FBI that the call is being monitored by a recording device. Depending on various laws in the jurisdiction(s), one may have to ask for a full name and explicit permission before proceeding with the conversation, otherwise the tape may be inadmissible in court proceedings (if one is envisioning the eventual need for those). Better still I would imagine to have the non-gunowning family member or friend do all the talking even in this case.
Sounds like we're in lawyer territory already on this... :-( Some kind esquire may be able to put together a FAQ on the topic for the benefit of those who live in the region...
You may want the cooperation of a neighbor since the tape and all locally kept copies will probably "disappear" permanently in the event of a warrant based search... along with all of one's legal weapons, of course... and computers, etc. ...