Open source software and hardware has become an accepted way of developing new and interesting applications in many information and communication technology domains: operating systems, databases, Web infrastructure, and applications. It's not surprising that with the increasing popularity of mobile handheld devices, users and researchers have explored the power of open approaches to providing innovative new applications and services in this domain. However, unlike personal computers and the Internet, mobile handsets were tightly controlled by mobile network operators (MNOs) who developed a vertical ecosystem by integrating the communication infrastructure, the handheld device hardware, and often the applications installed on those devices. The software and protocols running the mobile communications infrastructure and devices are often standardized by membership-only bodies, where large MNOs and manufacturers have a predominant influence. These players invest significant financial resources into shaping the industry along their vision to gain a competitive advantage. A current example is the ongoing battle about the dominant radio access technology for 4G cellular systems: LTE vs. Wimax. These trends have changed recently. Companies such as Google, Nokia, or Openmoko and Industry Alliances such as the Open Handset Alliance are providing the core building blocks, both in hardware as well as software, of increasingly open mobile devices. This issue of the OSBR reviews the relevant trends in the open mobile platform space from a number of perspectives. As the articles in these issue show, there is a lot of exciting ongoing work that brings the power of open source development to the mobile space. This trend is not just confined to the mobile devices as there are also efforts in the development of open mobile infrastructure elements and whole systems.