Sprint’s new iPhone 6s upgrade plan is the cheapest. You trade your smartphones and get a new iPhone 6s for just $15 per month.
With the Apple Store App there is no stalling. I would avoid using the website. This is the best method because it is fast, easy to use and you can even use Apple Pay. Ironically you will be using your old iPhone to buy your new iPhone. If you don’t already have the app. You can download it now. However if you no choice but to use the website make sure you have the order page up and ready to go. You can review all the carrier financing options and Apple’s iPhone Upgrade Plan via the Apple website. You can pre-order the iPhone 6s soon as the page is up.
If you cannot go through Apple and must go through hell, I mean your carrier
I’ve had a horrible time trying to get iPhones, iPads and pretty much anything Apple related at the carrier websites. However some luck people only use the carrier websites for pre-ordering. AT&T, Verizon, Sprint, and T-Mobile all have a dedicated pre-order page for the new iPhone.