  People in modern societies form different social networks through numerous
means of communication. These communication networks reflect different aspects
of human's societal structure. The billing records of calls among mobile phone
users enable us to construct a directed calling network (DCN) and its
Bonferroni network (SVDCN) in which the preferential communications are
statistically validated. Here we perform a comparative investigation of the
cliques of the original DCN and its SVDCN constructed from the calling records
of more than nine million individuals in Shanghai over a period of 110 days. We
find that the statistical properties of the cliques of the two calling networks
are qualitatively similar and the clique members in the DCN and the SVDCN
exhibit idiosyncratic behaviors quantitatively. Members in large cliques are
found to be spatially close to each other. Based on the clique degree profile
of each mobile phone user, the most active users in the two calling networks
can be classified in to several groups. The users in different groups are found
to have different calling behaviors. Our study unveils interesting
communication behaviors among mobile phone users that are densely connected to
each other.
