(Caller ID says "MASSACHUSETTES" (misspelling is their's not mine).  They leave no message.

I call after hours (using *67 to block my number).  The phone rings about 30 times.  Then I get the busy signal.

So they (poorly) spoof their caller ID and can't be called back.  Smells like a SCAM.

Over time I have received a bunch of calls from (508) 409 001x, all with the same misspelling, all suspected scammers.