A select group of iPhone users have reported that the touch-sensitive screen loses its sensitivity after an undefined period of time (mostly dependent on how heavy the usage is). The Finnish firm that developed the technology apparently foresaw this issue, since Apple is silently replacing the affected units without a lot of hoo-hah.While these issues don’t encompass the majority of the complaints about the iPhone, some believe this is only the beginning. It could become a problem for Apple if this turns out to be a widespread defect.