As expected the people at iFixit got a hold of an iPad 3G and then immediately tore it apart.
iFixit didn’t find much of anything new inside the iPad 3G, other than an expected 3G radio. If you are into the technical details of the radio, it supports UMTS/HSDPA on 850, 1900, and 2100 MHz and GSM/EDGE on 850, 900, 1800, and 1900 MHz.â€ The iPad 3G also has a black plastic strip along the top of the device which is there to aid in cellular reception.
One interesting tidbit that iFixit found, was that, while the iPad is handcuffed to AT&T with a MicroSim. Theoretically it could be used on any carrier with compatible wireless broadband, like T-Mobile. Some engineering individuals have already cut apart a T-Mobile SIM and have the iPad 3G running on T-Mobile Edge networks.
The 3G iPad also has an extra antenna cable which is for cellular radio reception. Other than the black plastic, extra antenna, micro-SIM card board and cell radio with antenna, the iPad 3G is practically the same device as the iPad WiFi.