SK Telecom said this week it is in talks with multiple device makers over handsets that will work with its LTE-A network when it goes live later this year, but it has yet to come to a final decision.

The operator has been demonstrating carrier aggregation (CA) at its stand during Mobile World Congress, having previously announced plans to commercially deploy the technology in September. By combining 10 MHz of its 850-MHz band spectrum with another 10 MHz of its 1800-MHz band spectrum, it will be able to deliver maximum downlink speeds of 150 Mbps.

"We have not had the terminals yet," said Sungho Moon, a senior R&D manager at SK Telecom.

For users to experience these speeds they require devices equipped with Category 4 (Cat 4) LTE modems. So far, Huawei has unveiled the first finished product capable of connecting at 150 Mbps, its Ascend P2 smartphone.

That's not to say the industry's other big names are not busy working on Cat 4 handsets.

"We plan to launch our first CA devices in 2013," said Chanwoo Park, vice president of Samsung's mobile product strategy, during a roundtable discussion at Mobile World Congress on Tuesday.

He explained one of the challenges that needed to be overcome was down to the sheer number of different frequency bands being used worldwide for LTE.

"3G has four major frequency bands, LTE has more than 20, and they are being used in more than 22 different combinations," said Park. "That makes it very hard to support all the customers around the world with one device."

However, that is precisely what Samsung plans to do, starting this year, he said.

Meanwhile, SK Telecom's Moon admitted that while CA can deliver very high throughput on the downlink, it currently cannot do the same to the uplink.

"The uplink [connection speed] is important as well," he said. "However, CA on the uplink is not supported yet."

There are some technologies that SK Telecom has already rolled out that have improved the uplink. One of those is coordinated multipoint (CoMP). It assigns the same cell ID to multiple sites, and coordinates traffic between them and the handset.