...for every Phone, you can use a "death-grip", with the difference,
by the not modified iPone4, the Problem will be happening in normal use.
The antennas of the Hd2 are in the lower part, right there where the hardware-bottons are.
Take both Hands, and enclose the lower half of the Phone to build a Faraday cage.
Certainly, it's helpful, you do this were the signal is bad
The very best method for instance is, to put the Phone into a microwave,
this is a very good Faraday cage and it has a window to look in;
but, don't turn it unintentional on, the HD2 will be demolished immediately