Try putting a wireless phone in one and see if it rings. Also try a cell phone or two. The microwave box is designed to stop the microwave freq (I think 2.1 gig but I don’t remember) and may not be as good a shield at lower freqs, like 900 MHz or higher freqs. They have to have a transparent window, and that will be a shield at a narrow range of freqs.
Aluminum or copper foil, though, can make a continuous conductive barrier all the way around your item with no, or few, leaky gaps, windows, or seals.
Come to think of it, your conventional oven may work well, too. You can test it by sticking a cell in it and calling it (I use a large shielded room with RF absorbing foam and a Watkins-Johnson receiver and a set of biconic antennas to do RF shield measurements, but sticking a cell inside works too).
I’m going to try that, thanks!
My DH crashed his motorcycle last week and his cellphone along with it. It can receive calls but nothing else.
I’m going to have some fun with that phone.