An iPhone User's Guide to 3G

The iPhone 3G's name immediately raises an obvious question, even to people who already own 3G phones: What the heck does 3G mean, beyond its abbreviation expansion to "third generation."

A 3G cellular telephone network offers something akin to wired broadband while away from a wire, whether you're anchored to a table, walking, or traveling at driving or train speeds. The 3G part refers to the evolution of the cell telephone network.

First-generation (1G) networks were all analog. If you're too young to remember the giant bricks of phones--which at one point required shoulder-harness cases, even--you might laugh to think of minutes, not hours of talk time, poor reception, and very crackly speech. 1G networks could handle very low-speed data on a good day.

Second-generation (2G) networks were all digital, but were developed just early enough that the Internet wasn't part of the thinking. 2G networks weren't optimized to move data around, just to reduce the network capacity needed to carry voice packets. Squeezing analog voice into data allowed networks to carry an order of magnitude more calls, which meant much more money in the days before unlimited plans of any kind.

2G networks can carry data, though. The CDMA (Code Division Multiple Access) technology that drives Sprint and Verizon Wireless's networks--and which is used in few other countries--offers dial-up modem speeds with 1xRTT, the slowest CDMA data standard. GSM (Global System for Mobile communication) networks offer both GSM (data transfer speeds of 9,600 to 1,4400 bps) and GPRS (General Packet Radio Services, up to dial-up modem speeds).

This brings us to 3G. (You may ask, what about 2.5G? I'll touch on that soon.) 3G was designed to deliver data as part of its very nature. It's optimized to carry bits that may or may not be voice bits. Verizon and Sprint chose a standard on the CDMA path called EVDO (Evolution Data Only). So far, it's gone through two revisions, from Rev. 0 (zero) to Rev. A. Rev. A is deployed almost everywhere that has 3G service on both networks.

AT&T chose to stick with GSM, and picked HSPA (High Speed Packet Access), a faster flavor in harmony with GSM equipment and networks. HSPA comes in separately organized standards as downlink (HSDPA) and uplink (HSUPA) flavors that are paired for service. AT&T initially deployed HSDPA with a slow uplink, but will finish upgrading its HSPA network to full HSUPA service this month.

AT&T's HSPA network is designed and enabled to allow simultaneous voice and data calls. Apple confirmed in a briefing with me that the iPhone 3G can browse the Web, retrieve e-mail, and find maps, all while you're talking (via speakerphone or Bluetooth headset, presumably). While Verizon and Sprint's EVDO Rev. A network can technically handle both tasks, too, the companies have focused on service-at-a-time: either data or voice, not both. A Verizon spokesperson said that the company is moving towards allowing both voice and data at once.

You might wonder why I haven't mentioned T-Mobile: the distant fourth among American carriers, T-Mobile didn't own spectrum capable of 3G services until a relatively recent spectrum auction. The company has just started to roll out a slow 3G standard in New York City, and expects to offer HSPA in the near future more broadly.

Now as to 2.5G, that 200 Kbps to 400 Kbps flavor bridges between 2G and 3G networks--which is primarily represented by the EDGE network the current iPhone uses--and was developed to accelerate 2G networks to be faster without the new technology and spectrum require for 3G networks. Second-and-a-half-generation doesn't make much sense grammatically, but it was a way for carriers to save money and have something faster when 3G deployments were delayed. (Future versions of EDGE are expected to be four times as fast through software updates to carrier base stations, although new chips are required for adapters and smartphones.)

The three 3G carriers claim their networks work in average ranges, where