No 4G. 3G and 3.5G will work just fine on T-Mobile network. Quote from Nokia's blog, "UPDATE: We incorrectly stated that the Nokia 808 PureView would only work with T-Mobile at 2G speeds. This was caused by an error in the spec sheet. We're sorry about any confusion. The Nokia 808 PureView works just fine with T-Mobile in the United States." http://nokia.ly/NIEMn4
What I mean is that LTE as currently implemented by ATT, Verizon, etc, in the US does not meet the technical specs for 4g (http://www.3gpp.org/ftp/Specs/html-info/36912.htm) especially the criterion of 100mb/s up when client is travelling at high speed, and 1gb/s when client is in fixed reference to station. LTE is not unambiguously 4g, it is grudgingly allowed to be called 4g by 3GPP who were somewhat taken aback when carriers started calling LTE 4g. True 4g is not expected worldwide until LTE10 is released (Parkvall & Astely. "The Evolution of LTE towards IMT-Advanced". Journal of Communications, 2009, 4 (3): 146-154. doi:10.4304/jcm.4.3.146-154). I think the term used currently for that version is LTE+ or LTE-Advanced or something like that. Tech documents regarding LTE etc cross my desk, though I am not an EE, so, it may be that newer tech specs have been pushed out, not sure. Your review, Tor, was rather technical so you may actually know more about the issue than I.
I get a 3.5g sign on my N8 nearly all the time, though, am heartily anticipating LTE! Maybe the TMetro mashup will bring it hard and fast. Maybe TMetro will completely migrate to VoLTE! But, I guess when Tmo gets its LTE or LTE+ or whatever, I won't be connecting on a (non-Windows) Nokia phone, certainly not the 808. Bummer.
I get the GSM buzz a tiny bit with the N8, especially on my car radio when the phone is about to ring (though nowhere near what I got with my old Sony phone, it was awful about the buzz). I didn't realize 3g didn't do that, I'll have to try!
As of November 2012, no carrier in the US has 4g. None of them. All major carriers, and certainly the GSM ones, have 3 and 3.5 g, which the 808 will show when connected. I use the N8 with Tmo and have 3.5g nearly everywhere in the LA/San Diego area (hills etc permitting).
I have intentionally turned off my 3g access for various purposes, which permits 2g access. If you are surfing the web and uploading 5mp pictures, you will be fine. If you want to video chat, skype, tether and watch netflix, you will need 3+g. And my N8, which operates across the exact same bands as the 808 does, works perfectly on Tmo. I have a 3.5g signal on my phone about 90% of the time.
Not sure what you mean. LTE (Long Term Evolution) is quite unambiguously a 4th generation technology, using separate bands/frequencies than 3G (UMTS/HSPDA/HSPA+) as well as 2G (GSM). Both AT&T and Verizon have by now quite extensive LTE networks. But of course, these are not supported by Symbian (neither the N8 nor the 808).
Sure, turning off 3G will save a bit of battery on most phones - and also work around a serious connectivity bug in the 808. However, I actually do the opposite - I select "3G only" (in Settings -> Connectivity -> Network). The reason is that when the phone is communicating over GSM, you'll often get an annoying "Buzzing" sound in nearby audio equipment (headphones, car stereo, etc). This is not the case with 3G.
The reason is a bit technical, it has to do with the fact that GSM is based on "Time Division, Multiple Access" (TDMA) technology, where there is great regularity between each time the phone emits signals, whereas for CDMA/W-CDMA technology (used in both UMTS and LTE), signal transmission intervals are more random.