  Mobile data traffic is growing exponentially and it is even more challenging
to distribute content efficiently while users are "on the move" such as in
public transport.The use of mobile devices for accessing content (e.g. videos)
while commuting are both expensive and unreliable, although it is becoming
common practice worldwide. Leveraging on the spatial and temporal correlation
of content popularity and users' diverse network connectivity, we propose a
novel content distribution system, \textit{uStash}, which guarantees better QoE
with regards to access delays and cost of usage. The proposed collaborative
download and content stashing schemes provide the uStash provider the
flexibility to control the cost of content access via cellular networks. We
model the uStash system in a probabilistic framework and thereby analytically
derive the optimal portions for collaborative downloading. Then, we validate
the proposed models using real-life trace driven simulations. In particular, we
use dataset from 22 inter-city buses running on 6 different routes and from a
mobile VoD service provider to show that uStash reduces the cost of monthly
cellular data by approximately 50\% and the expected delay for content access
by 60\% compared to content downloaded via users' cellular network connections.
