Currently anybody can buy unlocked GSM handsets in the US, just not directly from the carriers. I bought an unlocked Sony Ericsson P910a for use with Cingular/new At&T and it works very well. Unlocked phones are sold domestically through independent resellers and various online sources.
In Europe and Asia cell phones are sold primarily through independent vendors, not providers. As the result, people there can choose among 200 high-end wireless models in a single store. In the States, however, cell phones are sold by cheap mobile providers each of whom offers 10-20 old-fashioned models.
I will never believe that unlocked phones are not sold in the US because of the lack of demand. I know a lot of people here who are like me are ready to pay extra buck for getting a nice contract-free unlocked phone.
My best guess would be that there are some restrictions set by either the government or the cell phone manufacturers prohibiting anyone but providers selling cell phones on the US territory.
Does anyone know anything about it?