AT&T Inc. (NYSE: T) has revealed which U.S. cities will be getting its latest 3G network upgrade by the end of the year.

AT&T said Wednesday that it plans to start 3G services that can enable downloads at up to 7.2 Mbit/s in Charlotte, Chicago, Dallas, Houston, Los Angeles, and Miami by the end of the year. The operator says that it will deploy the faster 3G in "25 of the nation’s largest markets" by the end of next year and reach about 90 percent of its existing 3G network footprint by the end of 2011.

AT&T is using High Speed Packet Access (HSPA) 7.2 technology for the upgrade. This upgrade will likely offer average speeds of 3 Mbit/s to 4 Mbit/s data throughput on the downlink while the user is stationary, with bursts as high as 5.5 Mbit/s. Stationary uplink offers a throughput of around 1 Mbit/s. These figures drop when the 3G user is moving. (See AT&T Boosts 3G Networks and WiMax & LTE Meet the Real World.) AT&T will be adding additional backhaul at the HSPA sites to help with data traffic. "These backhaul connections add critical capacity to the network to support today’s unprecedented growth in mobile data traffic," the operator, which has been stung by capacity complaints recently, noted in a statement.

The HSPA upgrade will be AT&T's initial answer to Verizon Wireless 's Long Term Evolution (LTE) deployment and Clearwire LLC (Nasdaq: CLWR)'s mobile WiMax rollout. AT&T will start its own LTE deployment in 2011. (See CTIA: LTE, Android & Femtos and Verizon Makes LTE Connection in Boston & Seattle .)

AT&T is already pushing one advantage it expects to have over LTE in the coming year: the ready availability of HSPA 7.2 devices. The company expects to have six HSPA 7.2-compatible smartphones in its device portfolio by the end of the year, as well as two new laptop cards. (See LTE Phones Will Lag Behind Networks .)

In fact, the latest iPhone 3G S is already set up to support the HSPA 7.2 upgrade (See Apple's New Speedy iPhone.)

— Dan Jones, Site Editor, Unstrung