The next iPhone's unveiling date is safely locked down. Whether or not it arrives at every US carrier simultaneously is up in the air, however, and there's signs that Sprint's model might not ship as quickly as we'd like. Carrier training documents obtained by iSource, which we've since verified are real, would require that sales staff and technicians all be ready to offer "in-store Apple support" on October 15th, wrapping up their earliest training by the 30th -- that's up to a month after the introductory event, which would reduce the chances of a simultaneous launch if the first wave of iPhone availability is as close as the rumors would have you believe. Before you start plotting a carrier switch out of impatience, we'll add that there's a few disclaimers at play. First is simply that October 15th is a Monday, which is very out of step with Apple's habit of launching iPhones on Fridays. We'd see that day as the target for training alone, and that's assuming that Sprint needs everyone on the same page before the iPhone is in stores. More importantly, we know from our own tips that Sprint's internal calendar is in flux: the provider may not have concrete plans until after Apple's executives leave the event stage next week. As such, we'd treat the document leak more as a heads-up than a guarantee of trouble in Sprint's schedule.