I'm looking to buy a used iPhone here in Japan - either on Yahoo Auction, Craigslist, Mercari, etc. But with people easily throwing around terms like SIM-free, unlocked, and the like, I'm wondering if anyone residing here can give me a clear-cut explanation as to which of these terms I should be verifying prior to purchasing. Since I have no desire or intention to obtain service thru the big three - AU, Docomo or Softbank - I know to avoid anyone selling their phone which is locked to their carrier. I want to use one of the budget voice/data sim companies available in Japan. Would SIM-free and unlocked basically be the same end result? I can use the phone with any SIM card/service I wish? Is there any particular way I can verify that the device is SIM-free and/or unlocked? Thanks all.