AT&T today explained some of the key details behind a planned upgrade for its 3G network, including improvements to the infrastructure underneath. Having initially run a trial, the carrier now says it plans to start upgrading its network to 7.2Mbps HSPA this year and should have the faster service in place on all its connections by 2011. While actual speeds are likely to be lower, the peak is twice as fast as for the existing 3.6Mbps network.

The update is a prelude to 4G using the Long Term Evolution (LTE) standard, which AT&T reiterated is on track to start testing in 2010 and to go live in 2011.

To support the extra data use, AT&T says it has been and will be upgrading the backhaul, or infrastructure capacity, to support the technology. It has already been adding more support for 850MHz 3G, whose lower frequency has longer range and works better indoors, but now says it has also been adding fiber optic networking and extra capacity to "thousands" of cellular access points to handle the extra load. About 2,100 new cell sites are also going up in existing areas.

AT&T doesn't name the devices it expects to take advantage of the faster 3G but says both add-on modems and smartphones should be available later this year.

The speed and capacity upgrades partly corroborate reports of an iPhone-inspired upgrade to AT&T's network, which may be strained by video uploads made possible through the next-generation iPhone. They also potentially address frequent complaints about an overburdened 3G network that, in key cities like New York and San Francisco, has resulted in frequent dropped calls and 3G data often being slow or simply unavailable.

Multiple rumors have floated that Apple will give the next iPhone a 7.2Mbps 3G chipset from Infineon that will automatically use the added speed when it exists on the local 3G network.