I called this number back: says it's the National Trust for Historic Preservation. I didn't bother hanging around to actually speak to a human being, but I imagine it's some sort of fundraiser/telemarketing chicanery.
i finally called this number back this evening and spoke to a human. this is the number for the donor services department of MOCA the museum of contemporary art. the person was very nice and said they were probably just calling to say thank you for the donation. they seem to be having a problem with their auto-dial system, since i haven't made a donation and i haven't been a member for a couple of years. he said they'd take my number off the list, so hopefully that will be that. they were not trying to solicit donations via telephone.