Abstract: Social networking services, such as Facebook, Twitter, MySpace and Orkut, are changing our communication habits by introducing new tools that simplify and increase on-line interaction. The exemplary embodiments present methods for measuring the social strength among contacts on the basis of users' on-line interactions, which may be significantly used in real-time collaborative task management (e.g., inviting contacts for collaboration, selecting suitable tools for communication, prioritizing information flow). Moreover, exemplary embodiments provide a framework for developing new mobile social networking applications (social search client, smart dialer or contact applications) by extending the use of social ranking of contacts.