I just sent this Enhancement Request to Apple. I've reproduced it below:

Unlocked Verizon iPhone 4S To Work On U.S. GSM Carriers

This may be more of a problem with Verizon, but I really would love it if an unlocked Verizon iPhone 4S could be permitted to work on any GSM carrier in the world—including the United States. Currently, it only works on Verizon in the U.S. and GSM carriers internationally, but not AT&T, T-Mobile U.S., nor any other U.S. regional GSM carriers. I was going to buy an iPhone 4S, thinking that this was the dawn of the age of easy migration between wireless carriers, but upon learning about this crippling of the iPhone's enormous hardware potential, I have resolved to not purchase one. I also find it absurd that Verizon will not let an Apple-unlocked iPhone 4S be permitted on its network. This stifles innovation and reeks of monopolistic practices. If iPhone owners got fed up with AT&T's lack of expansive 3G coverage, they could switch to Verizon. If they got tired of Verizon's slow 3G data speeds, they could easily switch to AT&T or T-Mobile. If consumers were allowed to freely flow between carriers, the superior carrier would have more subscribers by nature and not by force. I'd prefer it if companies would bring about this change by themselves instead of legislation forcing the change. Either way, it must happen eventually. Apple has the power to protest these anti-competitive habits by allowing the activation of U.S. SIM cards in unlocked Verizon iPhone 4S's. I don't know if this request will actually do anything, but it makes me feel better to know that someone will see this and might even stop a moment to think, "What if..."

Go to http://www.apple.com/feedback/iphone.html to send your own Enhancement Request.