11. Apparatus, comprising: a memory, which is configured to hold a list of target users of a communication network and respective speech phrases that are characteristic of the target users; and a processor, which is configured to maintain the list in the memory, to select a plurality of candidate communication terminals from among multiple communication terminals in the communication network based on a selection criterion, to analyze speech that is communicated via the candidate communication terminals so as to identify one or more of the speech phrases in the speech, and to correlate one of the candidate communication terminals with a target user who is associated in the list with the identified speech phrases.
15. The apparatus according to claim 11 , wherein the processor is configured to select the candidate communication terminals using the selection criterion by choosing communication terminals that communicate with one or more predefined communication terminals.