Two-factor authentication using USSD. I've integrated a system like that with OpenLDAP. When you attempt to authenticate, a code gets displayed on your cellphon

Two-factor authentication using USSD. I've integrated a system like that with OpenLDAP. When you attempt to authenticate, a code gets displayed on your cellphone screen. You could also prompt the user to enter a code, etc. From what I gather it is cheaper to use than SMS, and there's no trace on the phone after the modal dialog is dismissed. Also - works with every handset.