AT&T adding LTE service to new markets
start building out its LTE signal next year. AT&T does expect to be mostly finished with its LTE construction by the end of 2013.
How fast is LTE service? About ten times faster than 3G. A song takes 4 seconds to download and a photo sent to your favorite social network will upload in 6 seconds. Apps download instantly and video streams quickly and clearly. AT&T has built its LTE network with "core elements" distributed throughout the country. This reduces latency, which is the delay you get when waiting for a response on the internet. Latency is reduced on AT&T's LTE pipeline, because your request has less distance to travel.
source: AT&T via AndroidCentral