AT&T has said that it plans to be "substantially complete" with its LTE rollout by summer 2014, but it looks like the big blue carrier has hit another network milestone before then. 

AT&T today confirmed to GigaOM that it has activated its LTE-Advanced service in multiple cities across the country. Unfortunately, the only market that AT&T would confirm that its LTE-A service is live in is Chicago. This LTE-A coverage utilizes a technique called carrier aggregation to combine different tidbits of spectrum — the 700MHz and 2100MHz frequencies, in Chicago's case — to push data over a 15MHz downlink that can produce theoretical download speeds of up to 110Mbps.

Of course, not just any ol' device can access this LTE-Advanced coverage. Right now AT&T only has one device that can utilize the LTE-A coverage: its Unite mobile hotspot. That's expected to change soon, though, as Samsung has announced that the Galaxy S5 will support carrier aggregation on select U.S. networks. AT&T also confirmed back at CES that the upcoming ASUS PadFone X will support LTE-Advanced and carrier aggregation.

AT&T has been talking up its plans for LTE-Advanced service since late 2011, so it's nice to hear that it's finally starting to roll the coverage out. Sure, it may not do much good when the only AT&T device that can utilize LTE-A is a mobile hotspot, but I'm betting that the AT&T subscribers in LTE-A-enabled markets will appreciate having the service live once they get their mitts on a compatible smartphone. Here's to hoping that AT&T can steadily keep its LTE-A rollout going and that it opens up a bit more about its LTE-A markets in the process.

Via GigaOM