Carriers already collect this data and sell it to anyone with the money to buy it. And they that request it.

In Person of Interest, the stars use other people's phones as remote microphones for listening in on conversations -- not just while they're on calls, but even when they're not using their phones.

That form of eavesdropping, like phone cloning, used to be a lot easier. Nowadays, I know of no viable generally available software tools that make it possible to listen through a phone's microphone when it's not being used for a call.

That said, all of the standard mobile phone spy tools listed above claim that they offer the ability to listen in on calls as they're taking place.