Question: *Background Information:* All materials have a resonant frequency, which is the frequency at which they are most easily excited (vibrated). That's how glass is shattered using high-pitched sounds.

Assume that there is a Boeing 747 flying through the air, and a fighter jet pulls up next to it. The pilot in the fighter jet takes out a device that emits a sound at the resonant frequency of the hull of the Boeing 747. 

**How much energy would it take (and is it possible) for the 747 to start vibrating so hard that it falls to pieces?**

Answer: 
It all depends on your construction of the Faraday cage... for a sufficiently well constructed cage (multilayer, continuous, RF gaskets on all seams) the answer is "yes". It's much easier to add another 3 dB of isolation than to double the power of your EMP generating device.

Imagine you have a cage that provides just 3 dB of shielding. If you put that cage inside another cage, you have 6 dB. And so it continues. This is one case where sufficient isolation is indeed possible (assuming you are far enough from the blast that the shield isn't mechanically compromised).
If you wrap your electronics in aluminium kitchen foil then the appropriate equation for the electric field transmission factor, that takes into account reflection from the foil and attenuation in the foil is
$$\frac{E\_t}{E\_i} \simeq 4 \frac{\eta\_{\rm Al}}{\eta\_0} \exp(-t/\delta) = 0.47 \omega^{-1/2} \exp(-22 \omega^{1/2} t),$$
where $t$ is the foil thickness and $\omega$ is the "frequency" of the EM radiation (see [Faraday cage in real life](https://physics.stackexchange.com/questions/160137/faraday-cage-in-real-life?lq=1) ). The transmitted power fraction would be the square of this.

Typical foil has $t \sim 3\times 10^{-5}$ m and the *lowest* frequencies have the highest transmission factors. According to [this extensive report](http://www.ferc.gov/industries/electric/indus-act/reliability/cybersecurity/ferc_meta-r-320.pdf), an E1 HEMP is less important than lightning strikes for frequencies below 1 MHz. At 1MHz ($\omega \sim 6 \times 10^6$ Hz), the formula above gives a transmission factor of $3\times 10^{-5}$. Given a typical HEMP E-field peak of around 50,000 V/m (same report), then this amount of attenuation is sufficient to reduce the signal to that typical from a strong FM radio station.

So my conclusion is that tinfoil would protect your phone from an EMP. However it is simply not practical or possible to *completely* enclose all electronic and electronic devices (e.g. they often need cables in or out or some kind of opening, that may leave them vulnerable).