Hey, excellent little enhancement!
I have a request, though, of course...
Would it be possible to update 650 to read "San Mateo, California" instead of Palo Alto?
650 covers all of San Mateo County. Palo Alto is about the southernmost point, Daly City is the northernmost (and most populous), and Redwood City is the county seat.
The city of San Mateo shares the county's name and is fairly centrally located, so even though it meets almost none of the criteria you use, it seems the most logical for a call coming from San Mateo County.
Thanks again for the wonderfulness!