GigaOM got to peek inside inside AT&T's Foundry innovation center in Texas this week, and the tour came with a special treat -- a first glimpse at how AT&T's upcoming LTE network might perform when the carrier flips the switch later this year. Where Verizon's existing network promises download speeds of between 5 and 12 megabits per second (though we've gotten far better and worse in practice), the publication witnessed a connection with 28.87Mbps download and 10.4Mbps upload speeds, using a MIMO antenna passing bits through both