[AT&T LG Optimus G] br0adband:
Las Vegas was actually the first city in the US where T-Mobile "flipped the switch" and turned on their 4G LTE service last November, a few weeks after the iPhone 5 came out (that was part of the reason, actually). I live in the downtown area and get somewhat "ok" coverage; T-Mobile's 4G HSPA+ is fine with me as I pull typical speeds well in excess of 10Mbps so it's a non-issue with me.

My LGOG can do the T-Mobile LTE without breaking a sweat, just requires me to add the fast.t-mobile.com APN (epc.t-mobile.com is fine for HSPA+ stuff, that might change in the future but I doubt it). I use their $30/month plan like so many others without any issues worth even mentioning.

If I misunderstood what you said and you were meaning that Sprint doesn't have 4G LTE here in Vegas, you'd be wrong on that count too (up to a point) but it depends on your area - they are currently testing it and I have a neighbor who noticed it last week on his Sprint device (think it's an S4, can't remember at the moment). We have a Sprint "switch" here in downtown about a half block from where we live and there's a cell site just off it so Sprint has the downtown area pretty saturated but it's not on 24/7, pretty sporadic as they're in the last testing stages before turning it on full time.

Anyway, as for the right sub-forum, it depends on which LGOG you have: the International version is the E975; the Sprint model is the LS975, and of course the AT&T model is the E970 which this specific sub-forum is about.

Choose where you want to participate by the model number/designation, or just participate in all of them I suppose. I'm going to guess you have the AT&T version since a) it's a GSM device (Sprint's is CDMA but uses the SIM card for LTE iirc), and b) the International version is factory unlocked from the gitgo anyway so...

You're in the right place, I'd say. ;)

The process is fairly simple:

- use the ZV9-ZVB-Universal-Root (search for it) and it'll root the phone in a few seconds then reboot it ready to go (make sure to upgrade the SuperSU if you stick with the stock ROM or intend to keep it around in a backup)

- use FreeGee (get it on Google Play Market) to unlock the bootloader and install the recovery (two versions of TWRP or a touch-based CWM 6.0.2.7 are the choices), make sure you back up the EFS info before and even after you do the unlocking, it can't hurt

- copy ROMs to the externalSD card (or internal, I suppose) and have at it

Very nice device overall, my personal recommendation would be to avoid that Nexus 4 conversion since a) you lose the microSD slot totally, and b) your storage gets cut in half from 16GB to 8GB (not sure if that's ever been resolved at this point). Realistically while it's a neat idea in practice, doing it gets you basically nothing of any real use. The ROMs available nowadays as compared to long ago when that conversion thing was first discovered make the necessity of "pure AOSP as a Nexus 4" pretty much useless at this point in time. The LGOG is one damned fine device, seriously, and doing some tweaking with a custom ROM and some kernel stuff will net you an even better device.

Last edit, I swear:

Pick a radio as well. The stock JB AT&T modem works just fine for me, there is a hybrid one (33_84 meaning it's the core of the older .33 radio (like the LTE support) merged with stuff from the newer .84 radio (which doesn't support LTE) - the hybrid of both gets you LTE support and the other newer goodies too. Note: the JB AT&T radio does support LTE just fine, obviously, and it works with T-Mobile's LTE support here in Vegas and elsewhere too so there's no logical reason to go swapping out with radios unless you just feel like testing things for yourself. The danger with the radio swapping is a potential brick if the flashing process corrupts something; you may not recover from it in terms of phone usage but then you'd have a nice clone of an iPod touch with quad cores and everything! :D

I tested the .33, .33-.84 hybrid, .48, and finally I just said the hell with it and put the stock AT&T JB radio back on it and haven't had any reason to change it again, it works just fine on 4G HSPA+ and LTE combined.