Yes this is true. You must be on wifi to use FaceTime. However, while I believe you still can't call other phones, FaceTime being an open source feature, inevidably you will eventally see this feature come to other phones too.
yes u can video call. no, not 2 any other phones. yes, only on wifi. no, not only 2 iPhone 4s. u can also do facetime w/ the newest iPod touchs that have cameras on them. :home: