So till now, AT&T was the only carrier that sold the sony smartphones, with the only exception I think was the playstation phone on verizon.
So the most logical thing for me is Sony to push again through AT&T, because:
1) They already have done business in the past, and have worked out the business side, so it's a safe bet, they might try to work deals with other carriers later through the year to have bigger exposure to the market.
2) It's a flagship phone, Sony will try to get it in the hands of as many people, the comment that it'll be available only full price in retail channels made me laugh
The situation is so heated, that they'll have to loose ton of money, just to try to snatch some market, to have a chance to stay a player in this market. They surely want to be in this market, why would they make the Z and show it at CES when no other big name was revealing top models - so they grab the spotlight at CES, and the phone doesn't get lost in all the announcements coming in Feb from the mobile congress.
3) AT&T would love to have another strong horse in the race so they are not dependent only on Apple or Samsung for the best devices they offer. For AT&T the bigger portfolio of manufacturers that want to move devices on their network gives them edge on pricing and other deal terms.
So yeah, I can bet money that in couple of weeks, there will be announcement/leak that AT&T will carry a Z/ZL phone, with LTE of course.