We have received calls from this number, as well as several other 650-723-XXXX.  At first we answered them, and it is indeed Stanford undergrads calling for donations.  We are both grads, so the second we would hang up from the first call, it would ring again for the other of us.  So far they have called fro mat least 9 different phone numbers, usually in the evening.  They never leave a message on the machine (and why would they?).