The call was from England. Business use trunk lines out of San Francisco to reduce costs to and from International affiliates. It is likely he knew your son and was using a business line to make a personal call.
I googled this number before answering, and found this thread so figured I would share what has happened to me with this #
I've started to received legitimate calls from a firm that I work with through this exchange. I believe it is a general number that appears when certain companies in Europe route their calls through California (i.e. not specific to any one person/company).
That's not to say there are not people placing suspicious calls through this number though.
(fyi - I googled this number before answering, and figured I would share what has happened to me in case it helps)