Does Alcatel One Touch Idol 3 show which LTE Band is used (e.g. 12)? I'm a T-Mobile US customer, and I'm quite interested in getting a phone with Band 12 support, and one that'll actually let me have a better understanding of the network and whether I'm receiving the benefit of having the upgraded phone with the Band 12 support.

As per https://sites.google.com/site/cellularbinder/compatible-phones and the specs of the phoe itself, Alcatel One Touch Idol 3 does appear to support LTE Band 12.

However, does it have the ability to show which band is presently being used, like some other non-Google phones can?  (I currently have a couple of Google Nexus phones, and am quite disappointed that there appears to be no way to see which exact bands of LTE or UMTS do they use.)
I currently have the Alcatel OneTouch Idol 3, and yes it does support band 12. In fact, my phone is currently using band 12 over band 4 which is what my OnePlus One was using, since it doesn't support band 12. 


One way to check is to download the LTE Discovery app. 
Or, open your phone's dialer and type *#*#4636#*#* -- this will open up Testing mode.


Go to Phone information and it will show which band your phone is using.  
See screenshots below. First two are from my Alcatel OneTouch Idol 3 and the last two are from my OnePlus One. As you can see, the Phone information mode for the OnePlus One does not show the LTE band for some reason. (Depends on the phone I guess.)

Also notice how band 4 is in use on the OnePlus One according to LTE Discovery and there are no bars, whereas the Idol 3 has 2 bars of Band 12 LTE. 



Note that these two phones are placed right next to each other.







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