Take my recent experience. We changed mobile carriers. Two of us were getting new iPhones, while the kids were keeping theirs.
Of the 4 phones, how many do you think could be called an easy change? None! That's right, 100% of the devices had some sort of issue.
But along the way, I had to back up the phone (a step the carrier recommended). To restore the phone from iTunes, we were required to use the oh-so-stupid two-factor authentication. And the iPad attached to the account was locked and I didn't know the password (but my son did). So it took longer than it should have to restore.
The second device we moved worked perfectly for about 12 hours, then it changed to "no service" and when I took the sim out and replaced it, it changed to "invalid sim." I realize this isn't technically an apple issue, but it was frustrating nevertheless. [edit: turns out it was an Apple issue not a SIM card issue. I had to plug the phone into my computer and let iTunes figure out that the phone needed an update. Once it ran, it worked on the new carrier again. Why didn’t anyone mention that?!]
Phone #3 was a new one. First order of business, back the old one up. For whatever reason, the machine I was using had many issues and it took several hours to create a backup. I learned later it was a bug in iTunes. So there's that. But wouldn't you know, our internet went out, and so the restoration process was harder than it should have been...especially when I came to realize the new phones REQUIRED the latest version of iTunes ... Which I couldn't download because, no internet.
Phone #4 was the real challenge. Another new phone. Now I had backed up the one it was replacing onto a computer a week or so before, because it wasn't working right and I didn't want to lose anything on it. I had thought about backing it up to iCloud as well, but I'll be honest and say that I could figure out how, precisely, the iCloud backup works. I find the documentation lacking. I also thought I backed up the photos to iCloud, but I missed a setting apparently, and didn't. So just as well.
I got the phone setup....and...where's the backup? It's not on the list to restore. So I selected one prior to that and restored. But where were my pictures, contacts, and other assorted items? Were they gone?
I poked around the Internet and learned some things. First, I learned that sometimes the backups via iTunes to a computer fail. More often than you might think. Most people don't notice because they don't try and restore. But when it happens to you and you've already reset the device? Oops. So the "pro tip" is to do the backup, and then to click the restore button to see if the backup is there.
I also learned that when the backup fails, the data still exists in a backups folder on your computer, and it's not hard to find; It's just missing the plist and manifest files that act as the index. What I did was to copy the missing files from another backup into this folder and I ran one of (actually several) of the iTunes backup explorer tools that are available. It allowed me to see that everything was, in fact, there.
But I didn't want to pay to recover everything. So instead I copied all the files >1MB to another folder and changed the extension to .jpg. Voila. There were my pictures. Yes the names are weird. And also yes, the exif data is missing. But I have pictures of the kids.
I looked for any gaps in my contact list and half finished text messages and picked them up and re-added them to the device manually.
It was work. Many hours of work. But it sure beat losing them.
Along the way, by the way, I turned off two-factor authentication to make things easier. It was NOT easier, and proved even harder. Frustrated, I turned it back on.
In all, the simple migration to a new carrier and upgrade to two new phones took somewhere between 20-24 hours. And a lot of grit and frustration.
And I ask again: why is this so freaking hard?!
