I'm the lead developer and maintainer for Tux Math and Tux Typing (http://tux4kids.alioth.debian.org), and I have also considered whether it is possible to offer Tux Math on the iPhone. I really detest Apple's policies regarding lock-down, but I have to admit that most kids love the iPhone, and there would be some educational value to having Tux Math there.
So, I talked to a lot of people, posted on some mailing lists that have knowledgable people, and came to the conclusion that it would be legally dubious to offer Tux Math as an iPhone app, although we might get away with it.
Tux Math has historically been a "GPLv2 or later" project, although many of our files suffer from some sloppiness of documentation. Almost all of the code comes from developers internal to the project. However, we have a few files that state "GPLv3 or later". Most of these are our own, and we could just relicense them however we want, but there is some outside code (maybe 1% or less of the code base) that is definitely "GPLv3 or later". So, the project as a whole has become "GPLv3 or later", even though almost all the code is GPLv2+. (We are consider cleaning up all the notices and moving all the files to GPLv3+).
My take on GPL3 and the iPhone is that they are pretty unequivocally incompatible. GPL2 has at least some arguable, ambiguous compatibility, IMHO, and there are certainly a few GPL2 apps in the App Store.
It should be noted that I have never read Apple's developer agreement, but what I have heard suggests it goes strongly against the principles of free software.
So, I reluctantly concluded that it would not be possible to put Tux Math on the iPhone under completely good faith actions.