Seems that the GPLv3 is not compatible with Apple AppStore constraints.
Here you have an interesting discussion: http://lwn.net/Articles/396535
Seems that the only possibility to use ESpeak in an application compatible with AppStore constraints is to release it with a double-license (GPLv3 and GPLv2 for iPhone for example). To do that all the ESpeak contributors must accept the change..... almost impossible !!!
I will give up this porting, it is pity because it is working well !
UPDATE-1: Thanks to Tejas Shah there are some good news. He found an application in Apple AppStore that uses eSpeak: SpeakToMe
So seems that is possible to have commercial application that are compliant with GPLv3 in AppStore.
I will continue with this port and publish soon the results on github.
UPDATE-2: The life is hard !