via engadget

We don't foresee Apple chasing folks down that have modified their iPhone or anything, but at least one case has proven that you may want to return your handset to stock before attempting to have it serviced. According to a recent report, a handset running "some third-party apps" and operating on T-Mobile was flat out rejected when it entered an Apple store for service. More specifically, the employee reportedly said that "the warranty was voided," and added that the mobile was "blacklisted" against future service or return. 'Course, the owner did manage to coerce the Apple store manager to allow a return (albeit with a 10-percent restocking fee added on), but we'd highly recommend reverting your iPhone to AT&T mode before begging for service just in case.