It looks like AT&T is the next carrier to follow the trend of eliminating subsidized phone contracts. According to leaked intel from the end of the year (Dec. 30th), AT&T plans to stop offering two year phone contracts starting January 8th, 2016.
An internal training document was leaked, detailing their new shifting strategy. According to the document any new and existing AT&T customers can only purchase a smartphone at full price, or through an AT&T Next payment plan from now on. This will apply to all phones, including smartphones and older dumb phones. It does appear that certain corporate users will be able to continue to get contract options.
The big takeaway from this is that AT&T will not even have a contract option for its existing customers who are on current contracts. That means switching devices or plans will be completely different for them.
In a later update, AT&T confirmed the veracity of this leaked document to the folks at Re/code. Here's a quote with the details,
"With $0 down for well-qualified customers, the ability to upgrade early and down-payment options available with even lower monthly installments, our customers are overwhelmingly choosing AT&T Next. Starting January 8, AT&T Next will be the primary way to get a new smartphone at AT&T."
Source: Engadget