Do cell phone carriers have the ability to listen in on/record their subscribers conversations?
Can they wiretap cell phones somehow? 
Yes they do.
Assuming this is everywhere. But I my country most telco’s are using a third-party organisation to do this on their behalve on requests of the the authorities.
They operate the network so surely they can tap in. There might be a difference though if your telco isn’t the network operator.
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Privacy is really hard to maintain, unfortunately. 
That’s why you should use Signal for calls if you want to avoid that.
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AFAIK vowifi is encrypted with IPsec tunnels, though the handshake could be intercepted by threat actors on the same VLAN, but other than that, MITM is difficult.
However, you can use VPN to prevent that as well.
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