Right now, if you want to find the digital versions of Fantastic Four and its sequel, you are going to have a very hard time as Twentieth-Century Fox has eliminated all digital versions of their original Fantastic Four films including ITunes and Amazon.
Eric Pullier reports in this article, the most likely reason is that Fox wants to build hunger for the new Fantastic Four film that is coming out in August. If people want a live action version of the original comic book family, they are just going to have to wait until August.
This is not seen as a retaliation against Marvel Comics, the original holders of the movie rights to Fantastic Four. Marvel Comics did recently cancel the Fantastic Four comic book. This could have been retaliation against Fox, the current holder of the movie rights. It is true that the comic book has not been selling very well for years.
Whatever the reason, if you want to download a digital version of the F4 films in the 2000s, you better hurry before the digital versions become as extinct as the dinosaurs.