You can import any image from the Camera Roll into Instagram. Because of this, you can take a regular phone photo, edit it with another app like PhotoForge or iPhoto, import it into Instagram, apply a filter, and proceed from there. PhotoForge is pretty nice because of its huge number of features. I would bet that many of the "point and shoot" camera apps would also save to the camera roll and therefore allow importation to Instagram as well. I know Hipstamatic does and it has some really cool vintage effects. Hope that helps!
