looking at their website, they don't sell unlocked iPhone 6
apple store is the only place to buy unlocked phones
barclay card offers 18 months no interest on purchases over 999 at the apple store
paypal / bill me later, offers 18 months no interest on any iPhone 6 or anything bought at the apple store
over $250
buy the verizon one from best buy
full price no activation
and it will be unlocked
if you buy an AT&T or t-mobile without activation at best buy, it will likely be locked to those carriers and you will need 40 days of tmobile service or 60 days of AT&T service to get an unlock