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Security / Is that a biometric device in your pocket? - Tech Update - ZDNet

Once you authenticate yourself via the telephone--with a password, your voice, or both-- the original application that asked for your username springs to life as though you had just entered your password with the keyboard or authenticated with local biometrics. The reason this is called out-of-band authentication is that the authentication data --- whether it was your password or your biometric information --- takes a different network path (or band) to the authentication server than does the username. The username goes over the Internet or a local area network, while the authentication data passes over the public telephone system. Waller claims that this sort of out-of-band authentication is much more secure than other forms where both the username and authentication data are essentially packaged together and travel across the same network.