The unit has to know where it is because in different locations AT&T has different wireless licenses. For example, in most parts of North and South Carolina, A

The unit has to know where it is because in different locations AT&T has different wireless licenses. For example, in most parts of North and South Carolina, AT&T owns the PCS B license and so the unit knows its location and knows that it can operate on those frequencies without interfering with another company's spectrum. If the unit was using the wireless spectrum of another company, that company could rightfully sue AT&T for causing interference with their equipment. And wireless spectrum wasn't sold nationally in this country so AT&T (or Verizon or whomever) has different licenses in different locations and the unit needs to know what it can use. Heck, the AT&T device needs to know what spectrum AT&T has offered for 3G usage in an area so as not to interfere with the GSM/EDGE signals. The reason you can't use it in another country isn't some plot to make it so you can't use domestic minutes overseas. It's because it would be illegal for AT&T to allow you to operate a wireless transmitter on another company's wireless spectrum. T-Mobile is a different case because they aren't using micro-cells. They're providing handsets that do WiFi and traditional wireless. As such, they can allow you to set up your WiFi device anywhere because WiFi spectrum isn't licensed. Sprint similarly has a device (the Airave) which is a micro-cell and uses a GPS unit to determine where you are. The trade-off is that you can only install a micro-cell where a company is licensed to operate, but it works with lots of phones -or- you go with WiFi and can put it anywhere, but you need a special WiFi-enabled phone to use it.