Methods and systems for monitoring communication of mobile communication terminals, such as cellular phones. An off-air monitoring system reconstructs both directions of a call conducted between two mobile terminals by receiving only downlink channels. The off-air monitoring system receives multiple downlink transmissions transmitted by base stations in a wireless communication network. The system uses the received downlink transmissions to reconstruct the bidirectional call content of calls conducted between wireless terminals. In order to reconstruct the bidirectional content of a given call, the system identifies and correlates the two downlink transmissions of that call from among the multiple received downlink transmissions.