Prior models had only AT&T as an option. However, last year also had a $50 a year data plan option with a cap of 250MB per month -- good for those who "usually" had wi-fi but needed cellular connectivity occassionally. Click on the data plan option links on Amazon.com's site (AT&T, Verizon) takes you to the carriers' typical data plan pages.
This year's models sport Amazon.com's Fire OS 3.0 "Mojito" platform, which is really a forked version of Jelly Bean, though it's unclear if that means 4.1, 4.2, or 4.3. Last year's model was built on Ice Cream Sandwich (Android 4.0).
Fire OS 3.0 is compatible with Android apps, but considering its heavy customization, as always it was "built" without Google's approval, so it's minus all the Google apps that folks have come to love (or hate). Included in that, however, is the Google Play app, which means that you can't install apps from Google's marketplace.
While Amazon.com has its own marketplace, the Amazon Appstore for Android, if you have purchased apps in Google Play, you will be forced to buy them again in the Amazon Appstore. There are, of course, ways around this, but they don't always work.
If, however, you are more involved with Amazon.com's ecosystem than Google's, this may not be an issue for you.
The Kindle Fire HDX 7-inch tablet starts at $229 (wi-fi only, 16GB), which is unsurprisingly the same price as Google's 2013 Nexus 7 tablet. The 8.9-inch version starts at $379 for the same storage and connectivity options. For LTE connectivity, you can add $100 to each price.
These models get an upgrade to 2.2Ghz Qualcomm Snapdragon 800 processors. They also have a special reading mode that will keep the tablet alive for 17 hours of uninterrupted reading.
The all-new Kindle Fire HD has the same display quality and processing speed of last year's high-end models and comes in at the breakthrough price point of only $139. The new Kindle Fire HD starts at $139 and is only available in a wi-fi only version.
In addition to all this, Fire OS 3.0 includes Mayday, which is a a 24/7 customer support module that allows HDX users (the HD does not have a microphone) to access Amazon.com support personnel. It works as follows:
Support personnel appear in a small video chat window. Not only can they converse with you, they can place arrows on your screen to direct you to items. End users can mute support personnel so they can neither hear your audio nor see your screen.
Mayday is free. The only requirement is access to the Internet.
The new Kindle Fire HD ships on Oct. 2, but can be pre-ordered now. The HDX versions ship on Oct. 18 in wi-fi only form, but not until Nov. 14 for the LTE versions.