If the phone that you are referring to is a landline and you have an extension in another room, all you have to do is to pick up the extension and you will be able to hear the conversation. You have to be careful though, because the other person may be able to hear a click, or background noises from the room that you are in like a TV or radio, and know what you are up to. If you mean a cell phone, this is a more difficult. It should also be remembered that it is also illegal and immoral.
There are some companies that claim they can help in these kinds of situations, though. FlexiSpy have software that you can install onto your phone as long as you have a BlackBerry, any type of Nokia 60, or a Windows phone. Ordinarily, the software would pick up the calls being made to the phone with the software installed on it and you would be able to listen to the conversation on your phone. In this instance, though, you want to listen to a conversation that is being made on your own phone so you will have to have the data sent to a computer so you can view it there.
Before you go to all these lengths to spy on somebody, perhaps you should examine your motives. If the reason why you want to listen to someone else's conversation is because you do not trust them, you are risking a lot. If they discover what you are up to, the lack of trust is just going to be exacerbated and the situation is going to get worse. Far better to resolve any underlying issues more openly and honestly than this underhand method.
There are some companies that claim they can help in these kinds of situations, though. FlexiSpy have software that you can install onto your phone as long as you have a BlackBerry, any type of Nokia 60, or a Windows phone. Ordinarily, the software would pick up the calls being made to the phone with the software installed on it and you would be able to listen to the conversation on your phone. In this instance, though, you want to listen to a conversation that is being made on your own phone so you will have to have the data sent to a computer so you can view it there.
Before you go to all these lengths to spy on somebody, perhaps you should examine your motives. If the reason why you want to listen to someone else's conversation is because you do not trust them, you are risking a lot. If they discover what you are up to, the lack of trust is just going to be exacerbated and the situation is going to get worse. Far better to resolve any underlying issues more openly and honestly than this underhand method.