[T-Mobile Samsung Galaxy Note 3] StarTAC Fan:
It refers to the following 4 frequencies: 850, 900, 1800, 1900 Mhz. The frequencies are not universally supported by the world's carriers. In North America, the 850 and 1900 are used, while Europe for example uses 900 and 1800. Usage in other regions vary. But to have "quad band GSM" capability means global compatibility, at least on 2G networks, and is therefore desirable.

GSM itself and closely associated technologies EDGE and GPRS (if it's GSM, then EDGE and GPRS are automatically implied) is also referred to 2G that preceded the 3G and 4G we are now using but backward compatible with 2G. Thus 3G and 4G phones such as the Galaxy Note 3 we are talking about here will work on the AT&T GSM network (which by the way uses 850 and 1900 Mhz frequencies) in addition to (I think this is your confusion) to AT&T's 3G and 4G frequencies.

Any modern, unlocked phones nowadays that has GSM capability will be quad band. So 2G is not an issue - any version of the phone will work on any carrier's 2G network. However, if you want to use AT&T's 3G and 4G network, you have to get a version of the phone that supports AT&T's 3G and/or 4G network. Only AT&T's version of the Note 3 (as well as T-Mobile's version for reasons pointed out above) will wholly work on AT&T's 3G and 4G networks.

In summary - I'm not sure if this is the question you wanted answered - yes the T Mo version will work on the entire AT&T 2G (GSM), 3G (UMTS/WCDMA/HSPA) and 4G (LTE) networks - whatever voice or data capabilities your AT&T plan requires. But the T Mo version has to be SIM (carrier) unlocked. From what I understand, this is the case.

WIND has traditionally used whatever version T-Mobile has used as they were exactly compatible with the WIND network and because WIND is too small of a company to impose their own specification on Samsung. They use the closet matching US model just like Bell, Rogers and Telus would use the AT&T version. Click on my link to [Q] Which USA Note 3 Variant to get? http://xdaforums.com/showthread.php?p=45794297#post45794297 and you will see the various model numbers of the Note 3. The "T" version is what WIND should carry (T for T Mobile surprise surprise) although the WIND Note 3 may come in their own orange retail box. Please note that WIND has traditionally SIM (carrier) locked their phones - you probably already know this but that means if you take it to the US, it'll roam on T-Mobile with WIND billing you. But if you did want to insert a T Mobile SIM, then you'd have to unlock it which, although can be done, would invalidate the warranty.

Also note that WIND doesn't use the quad GSM frequencies because it doesn't have a 2G network. It never built one because it started only in I think 2008 timeframe. Nor does it yet have a 4G network. So in Canada, it will use only the 3G 1700/2100 (AWS) capabilities of the T Mobile model. That's what I was talking about by WIND choosing the closet matching model for US carriers. But that's okay because if WIND does obtain part of that 700 MHz spectrum being auctioned by the CRTC, then their Note 3 would be 4G ready.

You're on WIND yet interested in the T Mo model because T Mo is taking pre-oders. Are you not aware WIND is also taking pre-orders since about September 23 through their Facebook account? https://www.facebook.com/WINDmobile/app_632884196731950