With, critically, one important difference: it now has two cellular antennas. This way if one loses signal, say, due to being accidentally bridged, the phone switches to the other. This is why the gaps in the metal band are different between the 4 and the 4S. (Compare them.)
It's also why Consumer Reports endorsed the 4S but not the 4. Because it doesn't have the problem. Because they fixed it.
See http://www.pcworld.com/article/241186/new_iphone_4s_antenna_...
