Today's the day that the iPhone 6S and iPhone 6S Plus are rolling out to first-day adopters. Thus begins a cycle of smartphone replacement (soon to be annual, apparently, given all the major U.S. carriers announcing plans that allow customers to turn in their phone for a brand-new replacement every year) that will play out over the next few months.
If you're an iPhone user or support iPhone users, you may find that transferring your data from an old phone to a new one is perhaps not Apple's strongest suit. The situation's gotten better, but there are still plenty of pitfalls.
Before you upgrade
Transferring to a new phone with a minimum of heartache starts with preparing your old phone for the transfer process. If you're using iOS 9, Apple recommends that you update all of your apps from the App Store before running a backup.
Pretty much every iOS device can back itself up to iCloud, Apple's online service. But while iCloud backups are convenient--they're automatic and require no user interaction--they've also got a major drawback. For security reasons, iCloud backups don't include the passwords you use for all of your Internet accounts. While you can get a new phone and just restore it conveniently from an iCloud backup, doing so will force you to look up and re-enter numerous passwords when you are finally up and running on your new device.
To minimize password-entering, instead back up your iPhone to a Mac or PC via iTunes. Yes, many (most?) of us have stopped tethering our phones to our computers and just download or stream everything directly from the Internet. It's certainly a more civilized approach to using an iPhone, but iTunes has one major advantage: It allows you to make a encrypted local backup that contains all of your passwords. Connect your iPhone to your computer, launch iTunes, click on the iPhone (you may need to unlock the device and tell it to trust the computer you're connecting to, as a security measure), be sure the Encrypt iPhone Backup option is checked, and click Back Up Now.
If there's an Apple Watch in the equation, things are even worse. Apple apparently hasn't bothered to build any phone-transfer system into Apple Watch. So before you get rid of your old phone, you'll need to launch the Apple Watch app and tap on Apple Watch: Unpair Apple Watch. Apple Watch data is regularly backed up, and when you re-pair the watch on your new phone it should come back with your settings and most of your data intact. (However, I lost several days of fitness data when I did this.)
After you upgrade
Once you get your new phone, attach it to the same computer and choose the option to restore it from an existing backup. This will restore much of your phone's data, though strangely it will still insist on downloading at least some apps from the app store. (This is really inconvenient--it would be nice if an iTunes backup really did include every last thing, to minimize time and data use.)
Using the encrypted-password approach, I didn't have to enter in a bunch of passwords, generate new single-use passwords, and reset all of my two-factor authentication settings. In fact, I was only asked for five major bits of interaction: I had to re-enter my Apple ID and password "to help set up iCloud." That makes sense--Apple wants you to connect to your Apple ID, and you should have to do that at least once. (And preferably only once, though Apple devices sure seem to ask you for your Apple ID password a lot.)
While I didn't need to re-enter my credit card information to re-enable Apple Pay on my new iPhone, I did need to provide verification by entering my card's security code, printed on the back of the physical card. I also had to request approval for access to my iCloud Keychain from another device associated with my Apple ID--I re-entered my Apple ID and password on my Mac and approved the new device. After that, I just needed to set up Siri (a new iOS 9 feature lets you train Apple's audio assistant to listen to just your voice) and approve a request to use Find My Friends, and I was up and running on a new device.
Which still needed an hour to download apps from the App Store. That part wasn't fun at all.