Besides working on their respective carriers, what are the similarities and differences between the AT&T iPhone 4 and Verizon iPhone 4?
Due to the differences between CDMA and GSM, the antenna notches have been moved around. There are also 4 now instead of 3, and as a result of adding a notch on the left side of the phone, the mute switch is slightly lower on the Verizon iPhone 4 than the AT&T iPhone 4, which could cause cases made for the AT&T iPhone 4 to not fit the Verizon iPhone 4 properly:
Though this may change in a future version of iOS, right now the Verizon iPhone 4 has a "Personal Hotspot" feature to share the data connection with up to 5 devices. In contrast, the AT&T iPhone 4 supports tethering through USB or Bluetooth only, and only to 1 device:
Finally, because the Verizon iPhone 4 runs on Verizon's CDMA, it does not support simultaneous data and voice, unlike the AT&T iPhone 4 which does over 3G.
Engadget summarized the differences...