The teardown experts at iFixIt have peeked inside 3G iPad, which carries a model number A1337. As you know, 3G iPad is basically the same device as the WiFi-only model, sans an added 3G circuitry and GPS sensor. Surprisingly, iFixIt noted, 3G iPad is unlocked and works on any cellular network, not just AT&Ts.
The only telling visual difference between 3G iPad and its WiFi counterpart is a thick black plastic window running across the top of the all-aluminum back. The sole purpose of this piece of plastic is to allow radio waves to pass through. According to iFixIt, 3G circuitry inside the device supports the same frequencies like the iPhone 3GS, including 7.2Mbps HSPA on AT&Ts 3G network:
The 3G iPad supports UMTS/HSDPA on 850, 1900, and 2100 MHz and GSM/EDGE on 850, 900, 1800, and 1900 MHz. Alas, in the US, AT&T is the only carrier that operates 3G on frequencies the iPad supports. T-Mobile should work, but only on the slower EDGE network.
Read more:
http://www.geek.com/articles/mobile...s-unlocked-3g-and-more-2010053/#ixzz0r3JsKDy2