  Electronic databases, from phone to emails logs, currently provide detailed
records of human communication patterns, offering novel avenues to map and
explore the structure of social and communication networks. Here we examine the
communication patterns of millions of mobile phone users, allowing us to
simultaneously study the local and the global structure of a society-wide
communication network. We observe a coupling between interaction strengths and
the network's local structure, with the counterintuitive consequence that
social networks are robust to the removal of the strong ties, but fall apart
following a phase transition if the weak ties are removed. We show that this
coupling significantly slows the diffusion process, resulting in dynamic
trapping of information in communities, and find that when it comes to
information diffusion, weak and strong ties are both simultaneously
ineffective.
