Advancements in Phone Number Verification at T-Mobile

This technical report outlines T-Mobile's initiative to enhance phone number verification by replacing insecure SMS One-Time Passwords (OTP) with a more secure network-based authentication system. The report details the evolution of T-Mobile's authentication methods, beginning with IP-based solutions and advancing to real-time SIM-based verification. This new approach leverages the unique credentials embedded in a device's SIM card or eSIM, allowing for possession-based verification that confirms the association between a device and its phone number. The report highlights the ease of integration for developers, who can adopt this enhanced authentication with minimal changes to their existing systems. Furthermore, it discusses the breakthrough of supporting SIM-based verification over both network and Wi-Fi connections, thereby ensuring consistent authentication regardless of the connection type. The advantages of this method include increased phishing resistance, improved user experience, and enhanced trust, particularly for industries managing sensitive data. Overall, T-Mobile aims to set a new standard in digital identity verification.