Are you saying you wrapped your cell good and it still rang when you called it. Its not a joke, scientific fact. If you are one of those suspicious of the gov listening in on you through your cell, you can make a tin foil case to store it until only you want to use it.
Why Does Aluminum Foil Block Cell Phone Signals? | eHow.com
Another example of a Faraday Cage
Why would it? Aluminum is not ferromagnetic. If I remember correctly, a Faraday Cage requires ferromagnetic material to work. Aluminum shouldn't change electromagnetic transmissions.