This paper applies the theoretical lens of infrastructure to study hacking practices that take issue with large-scale communica tion networks. The paper analyzes a series of hacks targeting the Global System for Mobile Communications (i.e., networks for mobile telephony) carried out by a cluster of people af filiated or sympathetic to the German Chaos Computer Club between 2001 and 2014. These hacks aim at acquiring propri etary knowledge and facilitating the autonomous operation of local mobile phone networks for communities, independent of corporate network providers. The contribution of this paper is to show how hacking of this kind can be understood as transgressive infrastructuring, a way of engaging critically with infrastructure that, in the case of GSM hacking, relied on three strategies—reverse engineering, re-implementation, and parallel operation, all of which aim at appropriating the targeted network intellectually, legally, functionally, and/or operationally. Aut...