This number was listed in a document received by mail. I am to call to be told more about a Sweepstakes prize they say I have won.  I suspect a scam, but am curious. The letter is from Publishers Clearing House. I wonder if this is true.

Some  of the common scams listed here, on 800notes, are  the "you won a prize" or "free grant" or "award" scams.
Those scams are described here:
http://phonehelp.2truth.com/facts.html

(That site also has a link to Amazon's phone blocker devices and apps, as well as a page showing various government sites that accept complaints or warn about scams.)