[peterwwillis]

I'm going to risk sounding like a dunce here, but IIRC some frequencies are more prone to bouncing off glass - for example in metropolitan cities with lots of high-rise buildings. While this is a detriment in the city, it could also be acting as a "satellite dish" making it easier to collect stay signals while also directing most of the transmission upward. Considering the antenna is supposed to be at the bottom of the phone the effect should be more pronounced as more of the glass can be used to direct the signal.

Am I crazy?

[snorkel]

Mobile devices tend to operate in the 700 to 900 MHz range which translates to a wavelengths of several inches, so it's quite possible the geometry of the drinking glass is providing a bit of focus to the signal.