The G1 is a hair taller than the iPhone, somewhat narrower, and noticeably thicker, measuring in at 4.60 inches x 2.16 inches x 0.62 inches compared to the iPhone's 4.5 inches x 2.4 inches x 0.48 inch. Despite that, the G1 fits comfortably into the hand and is perfectly comfortable to hold up to your ear.

The iPhone is lighter, 4.7 ounces to the G1's 5.6 ounces, but despite that Apple's handset feels more solid in your hand, no doubt at least partially due to the use of a harder plastic for the phone's back and the low number of moving parts. The G1's plastic feels cheaper, but the back is coated in that pleasant-feeling smooth liquid polymer finish that many case manufacturers use for their hard plastic shells these days.

At 3.2 inches diagonal, the screen on the G1 is smaller than the iPhone's 3.5 inch display, but they both sport the same 480 x 320 resolution. In addition to its 3G radio, which supports HSPA as well as quad-band EDGE/GSM/GPRS, the G1 also sports Bluetooth 2.0 EDR for hands-free devices (though, like the iPhone, it lacks support for stereo headphones), 802.11b/g Wi-Fi, and GPS.

The most obvious physical difference between the two is the G1's moving parts. While holding the phone in front of you in portrait mode, you can slide the whole screen assembly to the right, revealing the landscape-oriented physical keyboard. The slider action feels very solid--it has a pleasant ka-chunk sound and it springs into place--but a peek at the arm mechanism reveals that it's made of plastic, which makes me a little cautious about how well it will hold up over time.

There are a lot more physical controls on the G1 than on the iPhone: the bottom "chin" of the unit contains, from left to right, a green "Send" phone button, a Home button, a trackball, a Menu button above the trackball, a Back button, and a red "End" phone button. The right-hand side of the G1 has a small camera button--if you hold the G1 like a digital camera, it's in roughly the same position where you'd find the shutter button--and the left-hand side has volume up and down buttons. The back of the unit has the 3.2 megapixel camera and speaker and the bottom has the G1's data/power port, covered by a plastic dust cap, and the microphone. The G1's earpiece is located above the screen.