I want to buy someone an unlocked phone?

You just insert your sim. However, AT&T does know you've changed phones and, if the phone is a smart phone, a data plan will be added as soon as the network detects that a smart phone is being used. Unless you get an unlocked AT&T phone, there is no guarantee that that all functions will be supported.

Yes, that's generally how it works. For GSM phones, the carrier doesn't usually know or care what phone the SIM is in, and I suppose there is a way they can tell, but I doubt they bother looking.

Remember, the SIM only holds customer information. That's it. The phone it came from or goes to is inconsequential. As long as the new phone is unlocked, the SIM should work.

Samsung GT-i5800 Galaxy 3 Unlocked GSM Smartphone

3 Megapixel Camera

TFT capacitive touchscreen 3.2 inches

Wi-Fi 802.11 b/g/n and GPS Navigation

Bluetooth v3.0 with A2DP

Up to 15 h 30 min (2G) / Up to 7 h 15 min (3G). Up to 620 h (2G) / Up to 510 h (3G)

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