its illegal unless the other party is informed that you are recording.
Maybe.
Many states are "1 Party States" meaning that if at least 1 person on the call is aware that it is being recorded it is perfectly legal. The state I am is that way (South Carolina). You need to check your state laws. To complicate it, some states allow you to use the law of either state (in the case of an interstate call) and some mandate you adhere to their law. Again, it differs from state to state.