If you buy an iPhone, iPod touch, or iPad, and you happen to be a user of the iTunes Store in more than one country, take note which country's store you're viewing in iTunes when you plug in the device for the first time. This will be the country the device will register with, and you will be forever barred from purchasing or even updating free apps from anywhere else. The only way out is to delete everything on the device and do a full restore.
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From Eolake Stobblehouse