Ergative languages such as Niuean and languages with Austronesian-type voice morphology such as Tagalog show overt transitivity alternations based on not only the presence of an external argument but also the properties of the internal argument. In this paper, I propose that case assignment and overt voice alternations in these languages are different reflexes of the same interaction between the lexical features of Voice and the distribution of valued phi-features in the syntax. The result is an expanded system of Voice, varying along two dimensions: (i) external argument introduction, which is lexically specified on Voice, and (ii) the presence of a valued phi-feature, which is derived on Voice through feature sharing with lower verbal functional heads. The analysis presented for simple transitives in Austronesian-type voice languages is extended to account for productive causatives in Austronesian, which are proposed to involve Voice over Voice, as well as voice morphology in nominative-accusative languages such as Japanese.