Public relations is about the “ethical and strategic management of communication and relationships” (Johnston & Zawawi, 2004, p. 6) with individuals and groups (“publics”) important to an organization. At one time such publics could safely be thought of in relatively static terms such as geographic location. This is, of course, still possible—but such fixed categories are of diminishing importance when it comes to building relationships with modern publics and communicating organizational messages to them. Even the motor vehicles that facilitate physical movement are becoming “smarter” and converging with technologies such as mobile telephony, personal entertainment systems and handheld computing (Sherry & Urry, 2000, as cited in Sheller, 2002). This article aims to explore the idea that mobile technologies mean PR practitioners must rethink both the notion of publics and also how to relate to them. A “mobile PR” will undermine taken-for-granted views about the nature of media, messages, and the kinds of relationships public relations people can expect to create on behalf of their clients. Many practitioners are still getting to grips with the online public relations they have known—through activities such as arranging the building of corporate Web sites, monitoring online discussions relevant to client interests and both disseminating company information online and responding to inquiries about it. The idea of an even more flexible communications environment enabled by mobile technologies may seem very daunting. No-one has so far worked out how to “do” PR in this new communications climate—there are no prescriptions or generally accepted approaches. Yet if practitioners do not confront the dilemma of how to reach mobile audiences they risk becoming irrelevant to many clients who must communicate in the mobile space or face unacceptable decay in their business.