Have been receiving calls from this (and similar numbers: 415-504-3703, 415-504-3737) for some time now.  All are obviously from the San Francisco area and probably the same people using a range of numbers.

The reason I suspect this is the same organization is that when I do not answer (any of the calls) the calls are immediately followed by a call from "0".  What that is all about I have no idea, but because of reports related to similar numbers on this site and the fact that I do not answer calls from numbers I do not recognize, future calls will remain unanswered.