Ubiquitous computing technology holds the promise of enabling comprehensive localization services for any physical object that is augmented with an electronic tag. Given an adequate object sensing infrastructure (e.g., based on RFID readers or sensor networks), the location of an arbitrary object could be obtained at the touch of a button. However, the large effort involved in installing a ubiquitous infrastructure of interconnected object sensing devices is one of the major obstacles for implementing such attractive services. In this paper we describe an object management system using mobile phones, so called ubiquitous gateways, as the infrastructure components mediating between object sensors and global network server infrastructure. As part of our system architecture and implementation, we describe query services which allow to set up mobile phones for local object tracking as well as to configure the behaviour of the global network to implement a number of use cases concerned with the monitoring of physical objects.