Aluminum interfering with cell phone reception?

Factual Questions
1

So, I recently purchased the new GSM Palm Centro smartphone to replace my aging Treo 650. I really like the Centro, but none of the cases that are currently sold really meet my needs. I prefer to have the screen completely covered and protected, so I found and ordered this particular case, made of aluminum.

However, it seems that my phone’s reception seems to be somewhat worse when it’s in the case, and I’m guessing that’s due to the aluminum. When the phone is not in the case, I consistently get 3-4 bars, but when it is in the case, I get 0-1 bars. It’s such a shame, because I really do like the case, but I’m not sure if it’s worth keeping if the signal gets this badly degraded.

Can any physicists or metallurgy experts chime in? Does aluminum really interfere this strongly with GSM cell phone reception?

2

Any metal enclosure will tend to attenuate the signal to some extent; if you completely surround the antenna with metal, you’ll lose the signal altogether. RF does not pass through metals. Some of it is reflected and some is absorbed. This is why your microwave oven can contain a kilowatt of RF power and not expose you to significant levels.