[1] None of the phones I've wrapped in a single layer of standard
weight foil folded over once at the edge have been able to send or
receive calls / sms / data (cellular or wifi).
I'd been waiting for someone to say this. The RF power output is
pretty low to start with and almost any metal surrounding,
especially if it's grounded, would mean the surveillance device
would have to be with the phone... even if the cage leaked the
signal strength would be almost nil.
But don't forget the "Aftercare"... It ALWAYS works.