With the iPad 2 WiFi having bared its secrets already, it only seems fair that the WiFi + 3G model should have the same treatment. iFixit wasn't going to let a little thing like scarcity stop them from ripping asunder the WWAN-enabled tablet and peering at its cellular guts, and we can't say we blame them.
Inside things are much as you'd expect from the WiFi-only version, so that means the same chipsets, battery packs and radios as before. Apple has used two different modems, a Qualcomm MDM6600 for the CDMA version on Verizon, and an Infineon 337S3833 for the GSM version on AT&T.
Obviously the CDMA iPad 2 doesn't have a SIM slot, either, which on the GSM model is built into the headphone jack assembly. It's also a pretty poor show if you wanted to replace the WWAN boards, since they're soldered to the logic board.