3G Network Compatibility

• Verizon's iPhone is specifically adapted to run on Verizon's extensive 3G CDMA network, and as of 2011 is not 4G compatible. AT&T iPhone users who switch carriers to Verizon will have to change phones, as the AT&T iPhone runs only on AT&T's 3G UTMS and 2G GSM networks.
  
  

Network Limitations

• The decision to utilize Verizon's CDMA network meant limiting the 3G Verizon iPhone predominantly to North American markets. CDMA has considerably less coverage overseas than the GSM network, which is commonplace around the world.
  
  

Surf-and-Talk

• One of the biggest changes between AT&T's iteration of the iPhone and the Verizon iPhone is the loss of "talk-and-surf" capability. While the AT&T iPhone is capable of connecting to the Internet and transmitting data during a call, the Verizon version doesn't support this feature on it's 3G network as of March 2011.
  
  

Unlocking iPhones

• Because of the change in network, users trying to "unlock" an AT&T iPhone to run on the Verizon CDMA network will find that their device is not compatible. The change in network requires a complete change in internal 3G chips to make a Verizon iPhone. As a result, the AT&T iPhone cannot function on the Verizon network.