If you have to ask "Is this the..." in a headline, the answer is more often than not going to end up being no, so let's just make it perfectly clear right off the bat that this train is pulling in straight from Rumor Town, which in this case happens to be The Daily Mail. According to their sources, a third Sex and the City film is definitely moving along the tracks and that it will be a prequel (this part certainly has plenty of factual support for it, actually, as original SATC creator Candace Bushnell has written multiple novels based on the quartet of gals as teenagers/20-somethings).
And not only that, but the phantom project already knows who will play the younger versions of Sarah Jessica Parker, Kim Cattrall, Kristin Davis and Cynthia Nixon. They have the new foursome pegged as Elizabeth Olsen (Carrie), Blake Lively (Samantha), Emma Roberts (Miranda) and Selena Gomez (Charlotte).
Of course this is, as the Daily Mail themselves point out, not a Sex and the City movie that the current foursome want to have anything to do with. Several of the film's stars have gone on record saying that a prequel is entirely unnecessary since we already know so much about the gals, but just because they don't want to be replaced by younger models doesn't mean they won't be. Sex and the City is still very much so a viable brand (even the last film, which was murdered by critics and many fans alike, made nearly 3x its budget at the global box office), so don't expect HBO, New Line and series producer Michael Patrick King to be deadlocked against making a third film that goes against the wishes of its cast.
Of course, if they're going to give the 'ole Now and Then treatment to Carrie and the gals they're going to need the support of Sarah Jessica Parker and the gals. Will that ever happen? Who knows. The only question that's worth talking about at this point is whether or not a prequel is worth anyone's time. I still haven't seen the second film, so I'm already out of the SATC big screen loop (though I did catch part of it flipping through the channels the other day and was pleasantly wondering why I was watching a slow motion Alice Eve jog braless across a field), but I'd love to hear what some fans of the show/movies think about all of this.