Alcatel Lucent routers and other rooftop gear and antennas was recently installed to provision the LTE service in an old brick five-story building in Fell's Point, near the city's Inner Harbor.

Reporters using Samsung Galaxy S III smartphones recorded download speeds at up to 15Mbps and upload speeds at up to 6.5Mbps from the site. Sprint officials said most customers can expect somewhat slower speeds than those in newly activated markets, roughly 6Mbps to 8Mbps for downloads and 2Mbps to 3Mbps for uploads. Those speeds are expected to be consistent at a distance of up to about 1.5 miles from a cell site.

Baltimore is where Sprint launched fast Wimax 4G service in September 2008. Last year, Sprint decided to embrace LTE instead, and is also beefing up its 3G network under an ambitious nationwide multi-year program called Network Vision. Wimax will eventually be phased out, but Wimax devices will be supported through at least 2015, Sprint has said.

Sprint trails both og its bigger competitors, Verizon Wireless and AT&T, in deploying LTE, although it holds one big competitive distinction. "Our key differentiator on LTE is that we still offer unlimited data plans," Viet Chu, manager of 4G engineering for Sprint, said during the cell site tour.

Sprint's approach to LTE means that it will be able to support an array of LTE devices, including an LTE-ready iPhone 5 (or whatever the next-generation device will be called), which Apple is widely expected to announce in September.