What kind of pictures do you want to take? I find that I can take model photos for posting to forums perfectly fine using my iPad, for example, but if you want extreme closeups, great depth of field, etc. then you’ll probably need a bit of a higher-end camera.
The trick to using an iPad (or phone) for model pictures is, I think, to not try to get in too close. Since the actual photos you take have a much greater number of pixels than you need when posting to a forum, you can take the photos from further away and then crop them to what you actually need — right there on the tablet or phone if you want. This makes it easier to take decent photos, because when you’re not as close in, you can get more of the model in focus.