Attempting to pre-order Apple’s new iPhone 6 or iPhone 6 Plus this morning was an exercise in frustration for many customers, as Apple’s online store, which was scheduled to open at 12:01 AM PT today, didn’t actually open for more than two hours after the announced time. By then, many customers had started pre-ordering the new iPhones on the Apple Store app — also a hit-or-miss proposition for some. Inventory seemed to change suddenly,…