1. A method of advertising to a remote unit belonging to a user group of remote units, the method comprising: identifying a context associated with a communication sent to or received by a remote unit belonging to the user group of remote units; determining whether the identified context is associated with one or more advertisements by querying correlation data to identify advertisements having context that correlates to the identified context; when the identified context is associated with one or more advertisements, transmitting the one or more advertisements to at least one remote unit belonging to the user group.