AT&T has announced that they will put their flavor of third-generation (3G) cellular data networking in 80 more cities in the United States in 2008, for a total of 350 "leading markets." They're also finishing an upgrade for better upstream speeds that will be complete this year, and have restated commitment to the path to 4G, which will offer extremely high broadband speeds, faster than today's cable networks.

This clearly moves the timetable for a 3G iPhone further along, because two constraints kept Apple and AT&T from releasing such a phone. One was battery life and chip size, problems which are clearly either solved or on their way to being solved. The other was service. AT&T's little secret is that compared with competing 3G networks run by Verizon and Sprint Nextel, they had a smaller footprint and a lower speed. These upgrades should put them on par with those two firms. (T-Mobile has no 3G service yet; just EDGE. They bought additional spectrum at auction that should result in 3G services starting this year.)

It would be a little embarrassing to deploy a 3G iPhone that could transfer data at only EDGE speeds in large parts of the United States, especially since sales of the current 2.5G iPhone show that the device will spread far and wide, beyond just major cities. The further AT&T rollout removes that marketing dilemma.

Verizon and Sprint Nextel use CDMA technology for voice and data; CDMA is used primarily in the United States and in parts of Asia, although not exclusively in any country. AT&T and T-Mobile chose GSM, a standard used by a vastly larger population, including Europe.

The 3G version of CDMA chosen by Verizon and Sprint Nextel is known as EVDO (Evolution Data Only), and the latest revision - Rev. A - can provide average speeds of 450 to 800 Kbps downstream and 300 to 400 Kbps upstream. Peak rates are technically 3.1 Mbps downstream and 1.8 Mbps upstream, but that includes network overhead. It's not unusual to have a 2 Mbps downstream burst when downloading a large file, however. A future, planned Rev. B would boost raw rates by 50 percent, and would work even faster if larger swaths of frequency were devoted to it than are used today.

GSM's path is to High Speed Packet Access (HSPA), often called either HSDPA - D for downlink - or HSUPA - U for uplink. AT&T's announcement today included the news that they would have HSUPA fuly rolled out in 2008. This will let them claim 600 Kbps to 1.4 Mbps downstream and 500 to 800 Kbps upstream. The raw speed for AT&T's HSPA is 3.6 Mbps downstream and about 1.5 Mbps upstream. In Europe, a 7.2 Mbps HSDPA flavor has already started to appear, too, and future flavors will ramp up to 14 Mbps and higher, although more frequencies than currently used would be required, as well.

Another interesting part of AT&T's announcement is that they restated that they are on the path to use Long Term Evolution (LTE) as the basis of their future 4G network. While LTE is perhaps three years away from deployment, it's become the standard of choice. In the United States, AT&T, T-Mobile, and Verizon are committed to it. That's right - Verizon has decided to opt out of future CDMA improvements and switch camps. This has something to do with a minority ownership stake by Vodafone, a European GSM carrier, but it's also a notable technology choice for them.

Sprint Nextel remains the odd duck out, having chosen WiMax for its 4G network, but being in the interesting position of starting to roll out WiMax this year, giving them what they hope is a leg up on speed and network quality.

I'm sure that Apple knows they are one of the engines pushing AT&T's growth in data use - Wired recently reported that data use in cities like San Francisco tripled on AT&T's network after the iPhone appeared - and seeing a completed and ugpraded 3G network must make them more confident in releasing a new phone.