But, isn't intercepting communications using a fake cell tower a wiretap?
If evidence of the wiretap never needs to be entered into the official record, did it really exist in the first place?
The article doesn't actually mention what ICE is actually using the cell site simulators for. It's possible that they're only collecting IMSIs and not text/voice traffic, which might still be wiretapping, but it'd be more difficult to argue in front of a judge.
It used to be possible to just set up an analog receiver and you could listen to nearby cell phone calls.