I agree, theres very little chance of it being an iPhone motherboard. Looking at the previous articles of the ipad2 teardown and the crack open iphone 4s will show its likely to be an ipad motherboard. I think its a good idea to compare dual core and quad core CPUs, because more does not always mean better.

http://www.techrepublic.com/photos/apple-ipad-2-teardown/6201759?tag=thumbnail-view-selector;get-photo-roto

http://www.techrepublic.com/photos/cracking-open-the-apple-iphone-4s/6315300?tag=content;siu-container