AT&T launched commercial LTE service in its initial five markets – Atlanta, Chicago, Dallas, Houston and San Antonio. 
In a press release, AT&T said it plans to launch in a total of 15 or more markets by the end of the year.
AT&T said its 4G service is up to four times faster than 3G speeds. AT&T currently offers four 4G LTE-compatible devices: the HTC Jetstream tablet, the AT&T USBConnect Momentum 4G, the AT&T Mobile Hotspot Elevate 4G, and the AT&T USBConnect Adrenaline. http://www.att.com
