From other sources ...
Prefix (415) 251- is primarily in San Francisco, California, and includes 1,164 phone numbers.
(415) 251-9527 is a landline based in Ignacio, CA and is unpublished.
Ignacio, CA is about 30 km North of San Francisco.
Caller said he is calling from Bell Canada but if you probe he will admit he is calling from a subsidiary of Bell Canada but won't give you the name of his company. I have had a similar call from another phone number and the company sells cell phones. He says that you have won a free cell phone but there is nothing free about it as you have to sign on to a term with Bell Canada in order to qualify for the free phone. He also makes it sound like he has access to your personal information as he claims that you have been a good customer of Bell always paying your bills on time etc. This is the scary part.