It may look the same on the outside, but the guts seem to indicate more similarities to the next version than the current.

Amplify’d from arstechnica.com

iFixit has gotten its hands on the CDMA-equipped iPhone 4 and taken it apart to see what Apple has changed from the original GSM-based iPhone 4. Apple has swapped out the original vibrator for a revised "smoother" version, and made changes on the logic board to accommodate a new Qualcomm baseband processor compatible with CDMA networks like Verizon. The most interesting revelation, however, is that the Qualcomm chip that Apple used is capable of both CDMA and GSM communication. Read more at arstechnica.com