This paper addresses the issue of proxy-based data placement for mobile applications. The key idea is to use aggregated information about mobile users and their data request patterns to determine when, how frequently and how much data to be replicated on proxies. Specifically, we introduce a novel representation, Mobile Data Overlay (MDO) that captures aggregated mobile data access patterns. The underlying representation of the MDO utilizes an interval tree-based data structure in supporting efficient spatio-temporal operations on mobile data access information. We develop intelligent MDO reconfiguration (ReC-MDO) techniques that help determine proper granularity of data replication operation (i.e. appropriate segmentation of each data object) by extracting spatio-temporal locality of mobile data access patterns. The ReC-MDO approach effectively balances tradeoffs between replication cost and data access cost in making mobile data placement decisions on proxies. Through extensive experimentation, we demonstrate the superiority of our techniques over several popular data placement strategies.