Can I use an Otterbox Iphone 4 case for the iphone 4s???

You should get the 4S Defender, since it doesn't interfere with the camera optics and the light sensor location on the 4S. You can use the original 4 Defender, but there may be issues with your proximity sensor, and your camera.

You can tell by looking at the customer images. Look for the large cutouts by the speaker and camera. Here's a photo: http://www.amazon.com/gp/customer-media/product-gallery/B005SUHRH6/ref=cm_ciu_pd p_images_0?ie=UTF8&index=0&isremote=0