iPhone 4S launch: What's different this time?

After much fanfare, a minor pre-order meltdown, and what was perhaps the largest collection of Apple software updates to go out in a single week, the next arrives tomorrow.
If it feels like a long time since the went on sale, you're not mistaken. The iPhone 4S, Apple's follow-up to the iPhone 4, comes a few months later than Apple has typically released previous handsets, and it seems even longer given that leaks led to the world seeing the final design months before it was officially unveiled.
From the looks of it, Apple appears to have used that extra time to polish the latest version of its iOS software, which went out to users yesterday, as well as to ready Siri, the iPhone 4S that's being launched as an uncharacteristic "beta." That's not all that's different though. This year's launch brings a number of other changes, which we've detailed beneath.
More carriers
When the iPhone 4 launched (and every previous iPhone for that matter), the only carrier you could get it on in the U.S. was AT&T.