How do I know if my iPad 2 is 3g

The 3G model has a black plastic band at the top of the back surface. The wifi only model does not, it's all aluminum. Google for images of both.

Here's the various iPad model numbers and order numbers. The model numbers are on the back of the iPad

Apple iPad 2 (Wi-Fi Only) 16, 32, 64 GB

The wi-fi only iPad 2 configurations are assigned model number A1395.

MC769LL/A is the original order number for the 16 GB configuration in black. The 32 GB configuration in black is assigned MC770LL/A and the 64 GB configuration in black is assigned MC916LL/A. The original 16 GB, 32 GB and 64 GB configurations in white are assigned MC979LL/A, MC980LL/A, and MC981LL/A, respectively. On March 7, 2012, Apple discontinued the 32 GB and 64 GB configurations and assigned new order numbers of MC954LL/A and MC989LL/A for the black and white 16 GB configurations, respectively.

Apple iPad 2 (Wi-Fi/GSM/GPS AT&T) 16, 32, 64 GB

The Wi-Fi/GSM/GPS iPad 2 configurations are assigned model number A1396.

MC773LL/A is the original order number for the 16 GB configuration in black. The 32 GB configuration in black is assigned MC774LL/A and the 64 GB configuration in black is assigned MC775LL/A. The original 16 GB, 32 GB and 64 GB configurations in white are assigned MC982LL/A, MC983LL/A, and MC984LL/A, respectively. On March 7, 2012, Apple discontinued the 32 GB and 64 GB configurations and assigned new order numbers of MC957LL/A and MC992LL/A for the black and white 16 GB configurations, respectively.

Apple iPad 2 (Wi-Fi/CDMA/GPS Verizon) 16, 32, 64 GB

The Wi-Fi/CDMA/GPS iPad 2 configurations are assigned model number A1397.

MC755LL/A is the original order number for the 16 GB configuration in black. The 32 GB configuration in black is assigned MC763LL/A and the 64 GB configuration in black is assigned MC764LL/A. The original 16 GB, 32 GB and 64 GB configurations in white are assigned MC985LL/A, MC986LL/A, and MC987LL/A, respectively. On March 7, 2012, Apple discontinued the 32 GB and 64 GB configurations and assigned new order numbers of MC755LL/A and MC985LL/A for the black and white 16 GB configurations, respectively.

 Cheers, Tom 😉