Tired of typing four digits to unlock a smartphone? AT&T has a new solution called "voice biometrics," in which saying specific words could help unlock a phone or log into an email account. A log-in screen will ask you to say some words written on the screen, and will verify the accent and tone with its security records. Strong authentication, be it through voice biometrics or face recognition, is key to securing mobile devices, said Amanda Stent, a computational linguistics researcher at AT&T Labs. She believes speech has a big future in how humans interact with mobile devices.