Shown here are the logic board in the Wi-Fi, GSM, and CDMA models (listed from top to bottom).

iFixit's 6-inch metal ruler is shown to provide scaling.

The WWAN boards on the 3G models are connected to their logic boards via surface-mounted ribbon cables.

These cables make the WWAN board not user-replaceable, as the cables securely (and permanently) attach the WWAN board to the logic board.