I called the number back ( 415-363-9680 ).  Their outgoing message starts with "We're exempt from the Do Not Call List", but gave no company name.  In my humble opinion this is a red flag for SPAMMER!  Going on my blacklist.

They called with a caller ID that said Exchange Student and left no message. I do not want to bother calling them back. I do not think it is right for them to call and not leave a message. If they are begging for money for exchange students then they are not a legitimate
charity.

Called.  I have voice mail.  They did not leave a message.

Woman's voice, recorded, purportedly seeking hosts for exchange students.  Then she asked to press one number to talk to someone and another to be "added to our do not call list."  I did the latter and reported it to www.donotcall.gov.  Looks like they're doing enough of this that they'll get yelled at, and penalized unless they have some clever bankruptcy deal set up.

Did not answer and they did not leave a message.id listed the call as exchange student. First time for this one.do not know who they are or what they want. Will never answer this call