What's a collage app that can fit 20 pictures?

I want to create a collage, but I have a lot of pictures that I want to put in one. Most of the collage apps I've looked at only fit like 2-8 pictures, and it has to be on ITunes (I have an IPhone)

I know there's a new catch phrase around: "There's an app for that", but guess what… Not EVERYTHING is done via apps.

Sometimes, we still need to learn how to do something and need to make an effort to get to the result.
Other times, there really IS an app for it, but doing it yourself the "hard" way gives far superior results.

How to make a collage

If you type the words "free collage maker" into a Google searchbox, you will instantly get many hits, just like this: http://lmgtfy.com/?q=free+photo+collage

Here are a few examples:
http://www.photocollage.net/
http://www.photovisi.com/
http://www.kizoa.com/

Using a website is fine if you only want to make one collage, but if you do it regularly, you end up having to upload and then download again a whole bunch of photos. If your internet is down, you have nothing.
Also, resident programs are usually much better than free websites.

So in my opinion, you are better off with a resident program on your computer.
Again a simple Google search will give you plenty of options.
Picasa is one of those choices. I find its collage function awkward, but it is there and it is free, so why not try it.

The best collage maker by far is this one: http://site.lumapix.com/