The primary goal of this paper is to design a software replacement for a Subscriber Identity Module (SIM) based on the TCG MPWG Reference Architecture in order to access a mobile cellular network and its offered services. Therefore, we introduce a virtual software SIM (vSIM) with comparable usage and security characteristics like the traditional smartcard-based solution. Additionally, running a virtual SIM as a trusted and protected software on a mobile device allow significant expansion of services by introducing new usage scenarios and business models, cost reduction and more flexibility. Our approach demonstrates the substitutability of a SIM card with an adequate trusted software module supported and protected by a trustworthy operating system. In particular we propose several methods for authentication and enrollment of a subscriber.