I did pre-order my 6s too and I got it during the release date. I hope this time it goes the same way. Was there any delays for 7Plus orders during the release day last year? *I'm fishing for information here.
I just have a question: I upgraded my device to an iPhone 8 Plus during the pre-order date (Sept 15 @ 4:00AM). Is there a way I can know what number I am in the system? Will I even get my device during the release date? It's not that it highly matter...