Session initiation protocol (SIP) is a widely used authentication protocol for the Voice over IP communications. Over the years, several protocols have been proposed in the literature to strengthen the security of SIP. In this paper, we present an efficient elliptic curve cryptography (ECC)-based provably secure three-factor authentication and session key agreement scheme for SIP, which uses the identity, password, and personal biometrics of a user as three factors. Our scheme aims to resolve the security weaknesses and drawbacks in existing SIP authentication protocols. In addition, our scheme supports password and biometric update phase without involving the server and the user mobile device revocation phase in case the mobile device is lost/stolen. Formal security analysis under the standard model and the broadly accepted Burrows-Abadi-Needham logic ensures that the proposed scheme can withstand several known security attacks. The proposed scheme has also been analyzed informally. Simulation for formal security verification using the widely known automated validation of internet security protocols and applications tool shows the replay, and the man-in-the-middle attacks are protected by the scheme. High security and low communication and computation costs make the proposed scheme more suitable for practical application as compared with other existing related ECC-based schemes. Copyright (C) 2016 John Wiley & Sons, Ltd.