This coincides with my experiences: travelling to NY or SF turns my iPhone into an iPod touch. However, it works flawlessly in the very flat region of Virginia

This coincides with my experiences: travelling to NY or SF turns my iPhone into an iPod touch. However, it works flawlessly in the very flat region of Virginia where I live. It's my understanding that GSM is more prone to geographic disruption, hills in SF and buildings in NYC, than CDMA.