AT&T Inc. might just have had enough of all the complaints about its network being congested. It detailed its 3G network upgrade plans this week, saying it will go to 7.2mbps HSPA in six major markets by the end of the year.

Charlotte, Chicago, Dallas, Houston, Los Angeles and Miami are the markets slated to get supercharged this year. AT&T had previously announced plans to go to 7.2mbps (and the new iPhone 3G S is built to use it), but had been mum on where and when.

By the end of next year, the 7.2mbps upgrade will extend to a full 90 percent of its 3G footprint, at which point it will start in on deploying LTE, the 4G technology that’s expected to bring in the kinds of wireline-like speeds that will foster a whole new wireless data paradigm.

AT&T plans to add backhaul to further bolster network performance. And, in tandem with the HSPA upgrade, it’s rolling out more capacity in the 850 Mhz band for 3G.

“Our network is based on the predominant technology platform used by operators worldwide and has been tested by today’s most popular devices,” said John Stankey, CEO of AT&T Operations, in a statement. “That experience gives us an important advantage in developing and deploying new technologies to meet customers’ future needs.”