No, but if somebody like the NSA comes along with a request to intercept a specific package, or even a bunch of packages then customs will gladly turn them over. As was posted elsewhere in this thread, NSA has been known to do this in targeted cases and installed software into routers etc. before returning them to customs for delivery.
So it truly depends on whether an organization like the NSA has you on their radar.
The NSA is already known to have tapped into the fiber optic lines at an AT&T datacenter back in the early 2000’s. That sort of tap would generate absolutely massive amounts of data.
If they did something like that 20+ years ago then the volume & analysis isn’t the issue. It’s whether or not they decide they need to perform mass surveillance of mobile devices.