Comment GPL Ethics, Legality, and Morality (Score 1) 782
You are distributing the source code, as required, and therefore you are legally in the clear.
With respect to charging for the binaries, that is permitted by the license. I would however argue that this is bad form, and against the community spirit. The GPL is intended to benefit users and developers, and restrictions (e.g. a monetary charge, however nominal) on the access to binaries restricts the user community to those able or willing to pay or to rebuild. Rebuilding is a hassle, and subject to Apples $99 yearly charge at a minimum for anyone wishing to load it onto a iPhone device.
While I understand you wish to recoup the costs of porting and new feature development, I believe it is morally wrong to charge for a program that is free (in beer, and in speech) on the original platform(s) after porting it.
While the GPL permits charging for binaries, I believe it is uncommon and undesirable for free source code not to be matched by free access to the generated binaries of the program.