Need proof

He has an actual right to privacy, even though he's incarcerated, in his telephone conversations. Unless of course there's an investigation into criminal activity. Which talking to other women is not.

Not to lecture you, but recognize that the vast majority of inmates are in because of crimes that essentially boil down to either violence, some sort of dishonesty, or drug abuse/dealing. Or some combination thereof. Maybe think about that before worrying about whether this guy is talking to other women, and think about what's really an issue, and think about what kind of trouble you are probably buying with this 'relationship'.