Apple's reportedly put in big orders for the iPhone 6s but several reports suggest that yield could still be bad due to the Force Touch display technology that the iPhone 6s is widely expected to feature on board.
While this is an "S" version of the iPhone, it will still be in high demand this fall and you can expect some models to be harder to find in the days and weeks after the initial ordering process begins.
Stock at carrier locations and retailers is typically uneven so you'll want to have a backup plan in mind just in case you try and buy through Apple or someone else and the model (color, storage) you want is completely sold out.
If you want the iPhone 6s on the first day of availability, you'll probably want to pre-order.
This article may contain affiliate links. Click here for more details.