Just tried an EE (Orange) SIM in my VZW 128GB 6, and it worked just fine. No invalid SIM message or anything. So, not sure if this is a fluke or what on certain VZW devices. Same EE SIM also worked in my wife's VZW 5S, and my daughter's VZW 5 with no issue.
Edit: This thread at Apple indicates that this a known issue by senior advisors: "Finally I spoke with a Senior Adviser that submitted a request to the Apple Engineers. From my understanding this an error with the Apple Server that validates your iPhone's IMEI and or a Synchronization issue between Verizon Wireless's database and Apple's servers."
Thread:
https://discussions.apple.com/thread/6763925
Either way the issue exists and what I brought up earlier is still very much valid, its an Issue with Apple or Verizon, and until they don't resolve it, this issue will limit those devices to be in International LOCKED and Domestic UNLOCKED state.
I was looking around locally to buy a iPhone 6 just to check things out, didn't end up buying it but I bought a IMEI report on one that someone was selling and it too had the policy and sure enough when I tried my international SIM it said the Invalid SIM Error, so here is the policy to avoid:
US GSM/VZW N61/N56 Service Policy = Domestic Unlock / International Lock
US Verizon LTE MM N61/N56/N51/N48/N42 = Fully Factory Unlocked for US + Worldwide usage. As you know the N51/N48/N42 = 5S / 5C / 5 = Have no issues ever with working in US + Overseas
Ps. Thanks for sharing that thread, I want to start a thread but I know that there are too many people that will just take this in the wrong direction and tell me I don't know what I'm talking about.
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tl:dr You're wrong and have no proof to back it up.
read my above post and here is the proof:
https://discussions.apple.com/thread/6763925
Either way the issue exists and what I brought up earlier is still very much valid, its an Issue with Apple or Verizon, and until they don't resolve it, this issue will limit those devices to be in International LOCKED and Domestic UNLOCKED state and if you happen to be the sucker with a international locked VZW 6/6+ I wish you all the best dealing with Verizon or Apple lol....
You can put it how ever you want to, I KNOW I am right because issue exists.
Regardless if it exists due to a mistake and is in anyway violation of their FCC agreement. Fact is PHONE IS LOCKED against international use!
funny thing is even on the Apple thread there are so many people like YOU in disbelief.
Just wait and watch, the issue will become widely known and then there will be endless threads about it.
At the end of the day I'm sharing because I know this is a problem and point of sharing is so people can avoid dealing with this issue rather than knowing it but ignoring it and screwing someone else over in the long run if you happen to have one of those units and resell it.