Billions of users trust the telephone network with their most sensitive communications, including commerce, banking, industry, and personal communications. These users trust that the telephone network functions reliably despite the fact that telephones are the instrument of billions of dollars of fraud and abuse annually. This fraud is possible because telephony networks, including landline, cellular, and VoIP, have weak or non-existent abilities to identify and authenticate users. In this talk, we will examine how phone networks are being misused for authentication and secure communications. We will then see how new systems leveraging techniques from networking, cryptography, and signal processing can provide strong authentication of phone calls. These techniques will pave the way for a more trustworthy telephone infrastructure.