Well from what I've read... It will be considerably slimmer and redesigned, the home button is apparently changed which was revealed by the site that posted the parts and then pulled it, 4g LTE, a larger screen, better processor (which is the delay I think or the CPU cant remember i read it a while ago) and they also may use liquid metal instead of glass... Nothing is confirmed by apple all of this is just stories and leaks..
Nobody knows what Apple is going to do until Apple announces it. Really. 95% of the "secret" stuff posted on blogs is bs. In fact, there's a new blog I follow called Stupid Apple Rumors, in which a guy is actually tracking the things various blogs announce, followed by a rating of how accurate the rumor turned out to be. Most blogs have a C rating or below.
I can tell you as a FACT that most people INSIDE Apple do not know what the company is going to do. And they are well trained not to talk about they're doing to anyone.
The 4s was announced last October. It's sold like gangbusters ever since. I would bet all my chips that the next iPhone will be announced in the September/October timeframe, because having a new phone available in the Christmas quarter turned out very, very well for them last year.