In terms of appearance the sound buttons like volume and ring mute have been adjusted in order to make some space for the new antenna design. It is important to notice that current bumpers and cases having just a hole intended for side controls will not fit this new Verizon iPhone 4.
Now internally these two models are somewhat similar, as a matter of fact the new earlier ATT models used GSM technology and the new Verizon model will base upon CDMA processors. In other words now it is impossible to use an ATT version in Verizon network. One draw back in CDMA is that the user cannot simultaneously use the phone and the data connection.
In terms of mobile operating system ATT models will be receiving an update and for the Verizon models there will be a new iOS version.