The new iPad Verizon version also supports AT&T GSM network. However, the GSM version of the new iPad can’t perform on Verizon network.
A users who purchased Verizon iPad has confirmed on a Mac Forum that the new iPad includes a SIM slot to insert AT&T microSIM chip. According to this user the only thing required to activate the AT&T data plan is to adjust the APN parameters under Settings.app.
I was one of the first to obtain a Verizon iPad and can happily confirm that this is allowed! I used my AT&T iPhone 4S sim card and took out the Verizon sim, and data worked! You must apply the AT&T APN carrier settings before this works though.
It seems Apple is issuing unlocked Verizon models finally. However, the same is not possible on AT&T GSM models due to hardware limitations. The Verizon iPad will support only non-LTE bands (EDGE, 3G, HSPA+ 4G) on AT&T network.
Here is video showing how to swap the SIM cards and use the GSM network on iPad 3.
You can also get more updates by following us on Twitter, joining us on Google+ or by liking our Facebook Fanpage.