Then, yes, it will definitely work. Also, just as an example of how it works, you can add up to ten people's phone numbers on your microcell (as long as they are AT&T customers) so that they'll get reception from your microcell when visiting. So I've been able to plug in the number of a friend or family member who'll be visiting before they arrive (using AT&T's account management page) and when they get to my house, they usually have a signal on their phone right away. (Occassionally, however, they just need to turn the iPhone off, and then on again, for it to show up.) Again, this just shows that it's based on phone numbers registered in AT&T's account database.
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BTW, for what it's worth, after the 5.1 update, my iPhone now reads "AT&T MicroCell 4G" when at home, so it's definitely not reading my unlocked iPhone as a "2G" device.