[Windows Phone 8 General] iusauser:
This is only a simple summary I wanted to do about

There are many people who like to buy their smartphones from 3rd party vendors (ebay, and other on-line stores), so on.

Fortunately, there are several smartphones start with support for LTE networks

CANADA, U.S. (At&t, T-MOBILE), MEXICO (TELCEL), ARGENTINA (MOVISTAR), URUGUAY (ANTEL), PUERTO RICO (at&t), ETC.

To date are only four models of Windows Phone 8 with support for LTE networks in BC4 (the LTE Band Class 4, is the key band in many operators in America, but not to all) , whose band is used for LTE in Canada, Mexico Telcel LTE and the upcoming LTE network fron TMoUS

Should be mentioned that at&t has the license for the BC4, but not yet implemented (at least commercially), and so far at&t only uses its LTE in BC17 (the band 17 should not interest anyone outside of at&t). Even so, the at&t´s LTE devices releases are still very relevant to another countries like Mexico and another some countries in Latin America, becauser ther LTE devices that are made for at&t in addition to the band 17, also include support for LTE in the band 4, which is the band that is used by several american carriers. LTE devices from Canada work also in BC4

WP DEVICES WITH LTE IN BC4:

For now, WP8 devices supporting LTE Band 4, are:

-HTC Windows Phone 8x (check that it is the GSM version with LTE in BC4, not to be confused with Verizon´s HTC 8x, nor the global version without LTE). There are variants of 8Gb and 16Gb of storage.

-Samsung Ativ S GT-i8750 (not to be confused with the version GSM/CDMA). With variants of 16 or 32 GB of storage

-Nokia Lumia 920.2 [RM-820]. Not to be confused with the Lumia 920 RM-821 which supports other LTE bands (European and others)

-Nokia Lumia 820.2 [RM-824]. Not to be confused with the Lumia 820 RM-825 which has European and other LTE bands

Specifications:

http://pdadb.net/index.php?m=pdacomparer&id1=3808&id2=3814&id3=3914&id4=3985&id5=3906&id6=3860

At the moment, I have no information if some trick is needed to operate the LTE in another network for which it was designed, (of course, assuming that both the device and the network has the appropiated LTE band, but the smartphones mentioned meet the requirement of hardware essential to be able to function in carriers with LTE LTE in BC4

For example, so far, I know the requirements to enjoy the LTE if the device was not purchased with the operator (Telcel Mexico case for now, but can serve as a reference for other operators):

-A unlocked device, which support the band LTE 4 (or AWS LTE, which is the same)

-Being in an LTE coverage area

-A Version 6 SIM Card

-Postpaid plan

-That the operators´s system enable your cell phone line as "LTE user"

-May or may not, be needed a minor operation, as in the case of the Nexus 4 you have to enter a service menu to change settings related to LTE (like Nexus 4); or edit the APN settings (like as was done with the 3G)

Europe

In Europe, LTE bands are used:

BC7 (this is in 2600MHz) used for LTE in most countries of the EU; Australia, etc

BC20 (this is in 800MHz) some European countries already in use as in France, Germany, etc.. (although in the same territory also use BC7); Australia

BC3 (this is in 1800MHz). Only a few countries use this as LTE band are: Belgium, Denmark, Finland, etc (although in the same territory also use BC7 and BC20). Australia uses BC3 too.

WP8 DEVICES THAT HAVE LTE IN BC7, AND LTE IN BC20:

Lumia 920 [RM-821], not to be confused with the American version.

Lumia 820 [RM-825], not to be confused with the American version.

UPDATE: Added:

-HTC 8X LTE C625b (LTE BC7 and LTE BC3)

Specs:

http://pdadb.net/index.php?m=pdacomparer&id1=4039&id2=3859&id3=3858

Note: Some Latin American operators are deploying LTE networks in LTE frequency BC7, as Entel in Chile, UNE in Colombia, so they falls in the second case (European style)

sorry for my bad english