Methods and systems for monitoring mobile communication terminals. A correlation system selects candidate communication terminals to be monitored, and then attempts to identify whether the candidate terminals are indeed operated by target users. Following successful correlation of a candidate terminal with a target user, various surveillance actions can be performed with respect to the terminal. Correlation of candidate communication terminals with target users is based on identification of speech key-phrases. When evaluating a given candidate terminal, the system analyzes speech that is communicated via the candidate terminal and attempts to detect one or more of the speech key-phrases in the analyzed speech.