  The study of ontology (hidden variables) provides for a vital ground on which
significant non-classical features of quantum theory are revealed. One such
non-classical ontic-feature is preparation contextuality (PC) and advantage in
oblivious communication tasks is one of its operational signatures. This
article primarily pursues the ontic-feature underlying quantum advantage in
communication complexity (CC). We construct oblivious communication tasks
tailored to given CC problems. We upper-bound the classical success probability
of these oblivious communication tasks, obtaining preparation non-contextual
inequalities. We use the very states and measurements responsible for advantage
in CC problems along with the orthogonal mixtures of these states to
orchestrate an advantageous protocol for the associated oblivious communication
tasks and the violation of the associated inequalities, thereby unveiling PC.
To showcase the vitality of our results, we find a criterion for unbounded
violation of these inequalities and demonstrate the same for two widely studied
CC problems.
