ct The Wireless World Research Forum (WWRF) has identified ambient-awareness and device diversity as two key properties of applications and services in future mobile systems [1]. According to the WWRF, emerging applications for mobile devices will be adaptive, personalized, and context-aware. Ambient-awareness in particular is a crucial issue in indoor applications. Indeed, these applications need to know the physical location of users and other entities (i.e. services and devices), so that they can adapt their behaviour [2], and report it to users as well [3]. Moreover they will be delivered to different end-devices (phones, computers, info appliances) over diverse wireless networks. Despite this diversity, many mobile devices (e.g. smart-phones and PDAs) now support the Mobile Information Device Profile (MIDP) of the Java 2 Micro Edition (J2ME) platform. This platform provides a common yet flexible computing and communication environment that could be fitted for – and shared b...