How much you want to bet that you can pop in any sim card in the world and any verizon LTE phone will work?
get your info straight first.
All LTE Verizon phones come factory unlocked due to their 700mhz licensing.
iPhone 5S works with AT&T LTE and T-Mobile ( I didn't check LTE specs for HTC M8) but it would benefit HTC to have all bands to support LTE from AT&T & T-MO.
The only difference is Verizon won't take any other phone that is not certified for VZW so you can't take AT&T 5S to Verizon for example , from Verizon you can use your iPhone anywhere but sprint.
I wouldn't bet anything. I do it all the time.
When a Verizon rep says I'm not going to be able to use the smartphone when I buy it off contract, I just snicker.