AT&T is expected to announce Thursday that it will upgrade its Twin Cities cellphone network to full 4G data speeds, nearly two years after rival Verizon Wireless did so but ahead of competitors Sprint and T-Mobile.

For AT&T customers with newer smartphones or tablet computers, the upgrade to full 4G means download speeds should triple to about 12 million bits per second. Verizon has been offering those speeds in the Twin Cities since the end of 2010. Sprint and T-Mobile have promised to add full 4G data speeds here, but their timetable is unclear.

AT&T's network upgrade will bring the Twin Cities closer to the day where any cellphone connection to the Internet will be as fast as the average consumer cable or telephone company Internet service, and more widely available.

AT&T, which plans to make an announcement Thursday, disclosed in September that it planned to introduce 4G in the Twin Cities by year's end. Hardmon Williams, AT&T's vice president and general manager for Minnesota and the northern Plains, is expected to make the announcement at AT&T's Baker Center store in downtown Minneapolis.

Perhaps not coincidentally, Thursday's announcement coincides with this week's arrival in AT&T stores of the first 4G-capable tablet computer that uses a version of Microsoft's new Windows 8 operating system.

For the cellular industry, full 4G has been looming as the replacement for the widely available 3G that delivers download speeds of about 1 million bits per second. The 3G speed left many smartphone users waiting impatiently for websites, songs or video to download.

The key to Thursday's announcement is the phrase "full 4G service." AT&T has been claiming its existing network in the Twin Cities delivered 4G service, but in fact it was "4G-light," a technology whose speed was midway between 3G and full 4G. The full 4G service is based on a technology called LTE (Long Term Evolution), 10 times faster than 3G.

This fuzzy definition of what constitutes 4G service has allowed AT&T to claim it had more 4G wireless customers nationwide than Verizon, because it counted both metro areas that had full 4G and those that had 4G-light. Verizon, meanwhile, chose to deploy only the full 4G technology, and so had a smaller 4G coverage footprint nationwide. But, in terms of full 4G, Verizon leads nationally with 440 metro areas compared with AT&T's 88, according to figures provided by both firms. Sprint and T-Mobile lag well behind.

Steve Alexander • 612-673-4553