Hi,
The connectors are the same but as mentioned above, the 4S has a small round window for the ambient light sensor, adjacent to the purple/blue windows for the proximity sensor/s. So the 'automatic brightness' setting wont work.
Also the screw lugs for the surrounding frame are in different places.
I have even seen some cheaper units where a 4 screen/digitiser has been placed on a 4S frame and sold as a 4s!