Password Reset Server uses a third party called
to provide phone verification. To use the "Multifactor - Phone" question, you will need to sign up for an account with TeleSign. TeleSign charges $0.20 per call to a phone number in the United States.
Note that as of January 2011, TeleSign now requires a $100 monthly minimum. An alternative option without a monthly minimum is the ProxStop service.
Sign up for a free TeleSign account
Wait for them to approve your account (usually less than 24 hours)
Get your Customer Id and Authentication Id from TeleSign (under their
Add them to Password Reset Server (Administration | Configuration)
Add a "Multifactor - Phone" question to your Security Policy