"open source" ordinarily refers to code licensed under any of the licenses that are "approved" by the self-appointed board of the "Open Source Initiative". The license terms of those vary wildly and most of them do not give strong protections to users.
What is more specifically at stake here is code licensed under one of the GNU free software licenses that may have wound up in iPhone apps. To my (non-lawyerly) eyes, any programs that include code derived from a third party's GPL or LGPL licensed code are likely being violated unlawfully.
My point was to challenge the assertion that making source code available for apps, libraries, frameworks, etc. that use the iPhone sdk, is in violation of the apple terms.
Regarding L/GPL, which part do you think would be violated if one incorporated such code in an iPhone/ipad app, assuming one makes the resulting source code available?
Lastly, my original comment pointed out that one can port emacs and run on your device. Nobody can stop you because nobody would know.
Other comments have pointed out some factors of the L/GPL problems but I'll point out some and repeat that have not been mentioned yet.
Apps in the App Store are encumbered by Apple's right to disable use of the app by users who have already downloaded it. This is in clear violation of both GPL and LGPL.
Apparently (again, per the EFF) an app sold through the App Store may not be free distributed by other means. Another clear violation.
Also, you may not modify the app running on your apple device unless (and even then, only perhaps if) you sign the app dev agreement. That restriction on modifications is again in violation of GPL and LGPL (to, again, my non-lawyerly eyes and this is lay commentary, not legal advice).
We shall see. I'm confident that as a matter of principle the FSF would not support or endorse ports to these devices but what the EFF's discoveries make me wonder about is the extent of app store programs that are currently being distributed in violation of some of the third party code they use.
Finally, yes, I suppose that one may port GNU Emacs for personal use but, at the same time, it appears to me that one can not share the results lawfully, even with their friends. Taken to the extreme, perhaps everyone interested in running GNU Emacs (or XEmacs) on the iPad can do their own private port after paying Apple some money.
What is more specifically at stake here is code licensed under one of the GNU free software licenses that may have wound up in iPhone apps. To my (non-lawyerly) eyes, any programs that include code derived from a third party's GPL or LGPL licensed code are likely being violated unlawfully.