I got an email from Apple directly this morning saying I could pre-order my phone(s). I used the Apple Store (not App Store - they are totally different apps) to order my phones, so you can use that, or use the website directly and when you place the order you choose whether you want in-store or delivery service.
Assuming you are in the UK Apple are currently only pre ordering unlocked iPhone 5
no nano sim included on line via Apple.com/UK
I have not seen anything about buying on 21/9 except available from 08:00 at your local Apple store
get in the queue ( I ordered mine at 08:01 online this morning delivery on 21/9 )