Los Angeles Charlotte, Chicago, Dallas, Houston, Los Angeles and Miami will receive the upgrade using High Speed Packet Access 7.2 technology.
AT&T — Apple's network of choice for the iPhone in the U.S. — also plans to deploy HSPA 7.2 to about 90 percent of its 3G footprint by the end of 2011.
The HSPA 7.2 network can reach peak speeds of 7.2 mbps, although speed will be affected by where you are, which phone you own and the amount of traffic on the network. The peak speed of the current network is 3.6 mbps.
Later, AT&T plans to roll out 4G networks based on Long-Term Evolution technology (LTE). There is no reliable estimate of the LTE network speed, although numbers as high as 100 mbps have been bandied about.
"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. "That experience gives us an important advantage in developing and deploying new technologies to meet customers' future needs."
AT&T said it plans to invest up to $18 billion this year, with more than two-thirds going to wireless and broadband deployments.