Hello I have been thinking of buying a US unlocked model of an iPhone when in the US (I am a resident of Japan). But have been told that for some countries, at least for older models, this could be a problem. Would like to ask two questions related to the above topic. MODELS One is about model numbers. For example, iPhone 6s Plus is listed as Model A1634 in the US (as well as 1688 and A1687). But ONLY those latter models are listed as ok for Japan. Confusingly, Apple says " Models A1633 and A1634 also support LTE networks listed for Models A1688 and A1687" 1A) What does that mean as far as buying? Should I buy only 1687? 1B) Likewise with 6Plus--the US lists Model A1522 (GSM)Model A1522 but then Model A1524 (GSM) and Model A1524 (CDMA) are also given, also US but also Japan. Should I only buy 1524? I want to buy unlocked because I will use a MNVO (third party SIM). Probably linked either to Docomo or AU. It is my understanding that newer models are all sold unlocked but not necessarily older ones. Very confusing. WHERE TO BUY 2A) Gazelle does not list the model number. Right now there are no unlocked phones, but here is a link to one 6 PLUS.http://buy.gazelle.com/buy/used/iphone-6-plus-128gb-unlocked . How to know what you are buying? 2B) Swappa shows the model umber, such as here: https://swappa.com/buy/apple-iphone-6s-plus-a1634-unlocked (But as a Japan based business Paypal account holder, I don't have a Paypal Confirmed address--though I would ship to a resending service in the US. so maybe I cannot use them?) 2C) Glyde also does not seem to list the model. https://glyde.com/buy/used-Apple-iPhone-6S-Plus-16GB-Silver-ATT/12078900 A final question is about the relative merit of Glyde's verified vs New compared to Gazelle's claim of its own 30-point inspection, and Swappa's system of listing as Mint, new retail and new resale. Thank you.