You have tried this and it works?
Because, something you are not realizing is that there are 2 models of each iPhone. While some may appear on this list to have some of the same LTE bands, that does not mean it will work on any GSM or CDMA network. The phone signal is not carried over LTE, the data is. Apple does not list here the specific GSM & CDMA radio frequencies or hardware network compatibilities by technical data, only which carriers work with each unlocked model.
If you look on this list, you will see that while T-Mobile, Verizon & AT&T use the same model iPhone, Sprint works only with the other iPhone model. This is not because of the LTE bands, it is because of the GSM & CDMA capability which is not listed.
http://www.apple.com/iphone/LTE/
A1549/A1522 UNLOCKED only works with the carriers listed within this model number.
and
A1586/A1524 UNLOCKED only works with the carriers listed within this model number.
One of those models will not work with every single global network that uses the LTE bands listed, it is more complicated than that, as far as hardware goes, as I already tried to explain.
• From the notes on the above linked webpage:
(2) "Unlocked iPhone models may support LTE networks outside the country of purchase when using a valid SIM from a
supported carrier"
(3) "LTE band support is based on iPhone model number and configuration for either CDMA or GSM networks. LTE wireless service may not be available even if listed bands are supported by your carrier."
An unlocked iPhone 1586/1524 that works with 3, EE, O2 & Vodaphone in the UK will work with Sprint, US Cellular in the US, but, I would not trust it to work on AT&T, T-Mobile or Verizon.
If someone has actually used one of these phones bought in the UK and was able to fully use the phone on AT&T, T-Mobile or Verizon, then correct me.
(edit) NOTE: iphone 5c & 5s use different radio chips, don't support the same way as iPhone 6/6+.
Also, iPhone 5 was the first LTE iPhone and does not have the same radio chips as any newer iPhones (will not work in China). (This was main reason for 5c).