No message, just hung up also.

Fake "survey".  If you accept their invitation to take the survey, you are asked a few questions like, "Would you like an electric car if it would save you money?"  Once you take the survey, you have qualified as their "customer," and they feel they are free to hit you with an ad for a cruise or other junk.  Being their customer gets them off the hook, or so they think, because the law allows customers to be called without their permission.

Callback to this number finds that it is a Google Voice number, which means they just picked a Milwaukee number but that could be forwarded to anywhere.  Probably scammers since no one answers at the forwarded location.

...no.  If it's a "fake" survey, designed to get around the DNC registry requirements, and the callers later contact those same people about products or services, then the callers have broken the law and are liable for fines of up to $16,000.

This same number called me today and appeared to be a political call.  CID said "HALES COR WI", and it asked about voting.  Therefore it appears the same boiler room crew is used for many different kinds of annoying calls, some masquerading as political.