LTE 4G is far from universally available. In the United States, Verizon's 4G network is the current champ with respect to overall footprint. AT&T is hot on Verizon's trail, however, and has a growing LTE network of its own. Both of these network operators are lucky they had wallets deep enough to purchase 700-MHz spectrum from the FCC several years ago. This coveted spectrum is where both operate their 4G networks.

Sprint will launch a few LTE networks later this year, but won't be able to offer a significant LTE footprint until well into 2013. Same goes for poor old T-Mobile, which won't even launch LTE until 2013, let alone get a significant LTE footprint established.

Apple announced two LTE 4G versions of the new iPad, one for AT&T and one for Verizon Wireless. Both versions will include Wi-Fi (802.11a/b/g/n), Bluetooth 4.0 (this is kind of a big deal, by the way), and integrated GPS.

The AT&T-specific version will support LTE in the 700/2100-MHz bands, as well as UMTS/HSPA/HSPA+/DC-HSDPA in the 850/900/1900/-2100MHz bands, and GSM/EDGE in the 850/900/1800/1900-MHz band.

The Verizon version includes LTE in the 700-MHz band, CDMA EV-Do Rev. A in the 800/1900-MHz bands, and the same set of GSM, EDGE, UMTS, HSPA, HSPA+ and DC-HSDPA radios as the AT&T version.

[ Other tablet makers aren't taking Apple's criticisms lightly. Read iPad Rivals Fire Back to see what they had to say. ]

Where will the new iPad work and at what speeds? Obviously, it will work on the LTE 4G and legacy 3G networks of both AT&T and Verizon Wireless. Subscribers to either of these networks will also be able to take their iPad to countries around the world and have access to fast 3G--but not 4G--wireless service.

AT&T and Verizon get 4G versions, but Sprint and T-Mobile do not.

Technically, the new iPad supports Sprint's older 3G network (1900-MHz CDMA EV-DO Rev. A). There's no word from Apple, nor Sprint, whether customers will be able to activate the new iPad on Sprint's network. Though it is feasible, Sprint's iPhone 4S customers might have a thing or two to say about the speeds they are seeing on Sprint's 3G network. The new iPad will not support Sprint's dying Wi-Max network, nor its forthcoming LTE 4G network.

What about T-Mobile USA? Those who purchase the new iPad will be able to use in on T-Mobile's data networks, but to what degree is unclear. T-Mobile offers 2G services--think GSM and EDGE--in its 1900-MHz spectrum, and HSPA+ 3G/4G in the 1700-MHz band. According to the specs, support for 1700-MHz is missing in action from the new iPad. That means today, the new iPad can only be used on T-Mobile's slower 2G network.

There's one caveat, however. Last year, after AT&T announced plans to purchase T-Mobile USA, T-Mobile starting aligning its services with AT&T's. Chiefly, it has begun moving its HSPA+ service from the 1700-MHz band to the 1900-MHz band. It plans to further re-farm this 1900-MHz spectrum and move all its HSPA+ 3G/4G customers/devices to that spectrum. At some point in the future, it is feasible that the new iPad can offer HSPA+ service on T-Mobile's 1900-MHz spectrum. If and when that day might arrive, however, is a mystery.

For the time being, however, AT&T and Verizon Wireless are the only carriers in the United States that will offer a 4G version of the iPad.

As for the rest of the world, Apple has forsaken their 4G dreams. Though it supports the fastest version of 3G available around the globe, the only true 4G versions of the iPad are being offered in North America.

Windows is currently a nobody in the tablet market. That could change with the release of Windows 8, the first version designed for touch screens and the tablet form factor. With the new Metro user interface, Microsoft will try to serve both tablet and desktop markets. Can it succeed? Find out at our Byte webcast, What Impact Will Windows 8 Have On The Tablet Market?. It happens March 14. (Free registration required.)