AT&T will launch its LTE 4G network in five cities Sunday. Courtesy flickr/zombieite

AT&T will upgrade its wireless data network Sunday when the company's brand-new Long Term Evolution (LTE) 4G network goes live in five U.S. cities, including Atlanta, Chicago, Dallas, Houston, and San Antonio. According to AT&T's Architecture and Planning Executive Kris Rinne, the company will expand the network to 10 more markets by the end of 2011.

So what does this upgrade mean for AT&T's 90 million customers? Will the network be affected if the company's pending purchase of T-Mobile USA for $39 billion goes through? And what does this mean for Sprint and Verizon users? Here are six things you need to know about the AT&T's new-look wireless network.

  1. The new network is designed to cover 80 percent of the U.S. population; however, if AT&T's purchase of T-Mobile is successful, the company can expand its cell sites to rural areas and cover 97 percent of the population.
  2. AT&T won't sell a new data plan to access the network; rather, 4G LTE will be a perk thrown in on existing AT&T plans, says Rinne.
  3. While download speeds on AT&T's current 4G network max out around 6 megabits (Mb) per second, the new LTE network is capable of download speeds from 5 Mb to 12 Mb per second, making it possible to download a two-hour DVD-quality film in just 15 minutes.
  4. AT&T will have an LTE-capable phone by the year's end, says Rinne.
  5. Products compatible with the new 4G LTE network include the HTC Jetstream tablet, two USB data sticks, and a mobile Wi-Fi hotspot. AT&T will sell these devices with its standard non-phone data plan, which provides 5 GB of data for $50 a month. The lone exception is the tablet, which comes with 3 GB of data for $35 per month.
  6. Verizon and Sprint users have little to worry about. Currently, AT&T's 4G network is comparable to Verizon's and Sprint's 4G services in both speed and performance, but this would change drastically should T-Mobile join AT&T. Verizon has more radio spectrum available for LTE than AT&T, but if regulators let the company acquire T-Mobile, it can convert some of the 3G's spectrum to LTE and vastly expand its coverage.

No one knows if Apple's next iPhone will be LTE-capable when it launches, but most analysts don't expect this to be the case. Both companies declined to comment.