Originally Posted by Deeg

It is the same situation as making consensually monitored phone calls. If the CBP officers had asked the Thai woman to call the US citizen and allow the call to be recorded (without the US citizen's knowledge or consent) it would have been perfectly legal, without any court order. The reasoning is the same: when having a phone conversation, you take the risk that the other party is sharing the conversation with others. If that other party chooses to share the conversation with the government, you have no recourse.