(1) a government is already specifically interested in you or the person you're talking to when you have your conversation: both the fact of the conversation and the content of the conversation can probably be captured pretty easily.
(2) no government is specifically interested in you prior to your conversation, but you take no special precautions: the content is probably secure, it's probably not being recorded, but your location is probably recorded so if you later become a target of interest then the fact of your meeting is likely to be recoverable.
(3) no government is specifically interested in you prior to your conversation, and you take precautions (being careful about when and where you meet, and not bringing your phone): probably your conversation is reasonably secure.
