GSM is the most widely used mobile standard—210 countries—and by AT&T and T-Mobile in the US. What's groovy about GSM is that any device that'll take a SIM card—"subscriber identity module" is a chip that identifies you to the network and allows you to get on—can get you on a local network. Hence the market for "unlocked" phones that aren't tied to any carrier, which you can just pop an AT&T or T-Mobile SIM card in. It's also AT&T's response to Verizon's open initiative: GSM networks are technically already open.

CDMA is a competing voice-and-data standard that is smaller in distribution—but highly prevalent in Korea, Japan, South America and the US, on the networks of Verizon Wireless and Sprint (including MVNOs such as Helio and Virgin Mobile). CDMA is actually more efficient in terms of the way it uses channels, but it doesn't have GSM's "open" advantage of SIM card swapping. (This is why you can't take your iPhone to Verizon.)

2G refers to any second-generation networks—like CDMA and GSM/GPRS—that are digital, and not analog (which would be 1G). It's mostly for voice, but there's some slow data, too. (Remember WAP?)

2.5G are data upgrades to 2G networks that allow for faster data transfer. EDGE is the best known, used by T-Mobile and AT&T (and the bane of iPhone owners everywhere) and a transitional tech to 3G. Still pretty pokey, topping out at 200kbps downstream real world. Verizon and Sprint have a 2.5G technology called 1XRTT.

3G Now we're talkin'. Third generation is what we finally call "mobile broadband," with the potential for early DSL-like speeds. In the US, this involves two standards: the CDMA-based EV-DO for Verizon and Sprint, and HSPA for AT&T (running now) and T-Mobile (coming this year). Japan, parts of Asia and Europe also make use of W-CDMA. Despite the name, it's actually a GSM technology developed by NTT DoCoMo. For Americans this doesn't matter and only confuses things, so forgetaboutit.

HSPA High-Speed Packet Access is the umbrella term for two complementary GSM technologies, HSDPA and HSUPA, with the D and U standing for "downlink" and "uplink" respectively. Currently HSDPA can pull down info at speeds up to 14.4Mbps, but in the US it's more like 3.6, and only under amazing conditions. AT&T plans to hit 7.2 later this year. HSUPA is an add-on to HSDPA, rolling out in the US this year, which can transmit data at up to 5.7 Mbps, up from 384Kbps.

EV-DO is CDMA's 3G data service, used by Sprint and Verizon. There are different revisions, called Revs. The latest, Rev. A, is capable of 3.1Mbps downstream and 1.8Mbps up in ideal conditions. Though its specs are not as hot as HSPA, it is the most robust and widespread 3G network currently in the US.

4G is the near future of wireless data, with download speeds equivalent to or faster than most US broadband networks.

WiMax is 4G ultra-high-speed mobile broadband developed by Intel, Motorola and Samsung. In the US, Sprint is the only carrier planning to deploy it nationwide. WiMax promises incredible long range and connectivity on par with what you can get at home—think of it as Wi-Fi on 'roids. It was supposed to roll out hard this year, but Sprint has been having a lot of internal problems, necessitating cash injections from partners like Intel. Consequently, you probably won't see WiMax till '09 or '10.

LTE Long-Term Evolution is the other major 4G ultra-high-speed mobile data dealio. It's a GSM-based technology, and quickly emerging as the dominant next-gen standard, in part thanks to WiMax's stupor and Verizon's adoption of it. Though Verizon and AT&T have competing formats currently (CDMA and GSM respectively), both pledge to roll out LTE in the US. Verizon will do this as an overlay to its current network, meaning both CDMA phones and new LTE devices will work throughout the footprint. You'll start seeing LTE in the US in 2010 with mass coverage by 2012.

We skipped over some acronyms, and sped past others, but this should be all you really need to know to navigate Giz's mobile device coverage, so do yourself a favor and bookmark it.

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