If the phone was purchased sim free \ unlocked, then it will take any (global) sim, phones are never logged to a country.
PUK (Personal Unlocking Code), relate to SIM's not phines, so it sounds like your friend has locked their sim not their phone as they didnt know the sim pin.
The fact you have put EE UK sim in the phone and its working, to double check its unlocked I would take it back to care phone warehouse and ask them to put a test sim in it for Vodafone or O2 and check it works, if it does your friends just needs to call their service provider up and request the PUK code for their SIM.
You can ignore the instructions they are miss leading, phones are not locked to countries.
It takes 5 minutes for the phone and sim to register in the country\region when first used, after which point the phone should work as expected, but you can take any sim unlocked phone to any country, put in the sim and providing it supports the bandwidth frequency in the country the phone will work.
Please let me know if you need anything clarified or have a follow up question.
Ok so now we have established its a sim issue not a phone issue, if your friend knows their mobile phone number this will be sufficient for the service provider to look up the sim number.
Another option is for your friend to phone up their service provider and say they have lost their sim and require a new one to be sent out, this new sim not only will have the same phone number but will also be unlocked.
Ok so this isnt a PUK lock, and you are right there is a region lock, for some reason Samsung has setup this feature in 2013, but its not been flagged to me before as one its only one manufacture and secondly only applies to sims out side the EU (for UK phones).
As you have have suggested a 5 minute call should allow you to unlock the region lock, have you placed\received a 5 minute call using a UK sim?
The stick on the box should explain this "European Model: This product should be activated with a SIM card issued from a mobile operator within Europe. (as defined EU/EEA, Switzerland and the following Non-EEA countries Albania, Andorra, Bosnia and Herzegovina, Former Yugoslav Republic of Macedonia (F.Y.R.O.M), Monaco, Montenegro, San Marino, Serbia and Vatican City.) To use SIM cards from other regions, a cumulative call over five minutes must first be made with the SIM card from European operators."If you have not placed \ received a 5 minute call I can call the mobile number you have in the phone now for 6 minutes, so you dont incur any cost, if you would like me to do this please advise me of your phone number.
Understood this shouldn't cause an issue, I have spoken to a colleague he advised that once you have made a 5 minute call (even after locking the phone), the third party sim should work.
Can you advise the exact error message you see when a non-EU sim is inserted, as he wants to ensure we are not muddying the waters by trying to use a sim which is locked and needs PUK.
We believe the device is ready to be unlocked (and you have not caused any damage by first using a non EU sim), to double check I would place a further 10 minute call using the UK sim while in the UK.
You then need to get a non EU sim to unlock the phone, by inserting the sim in the phone it should come up with an option advising its locked and have the option to 'dismiss' or 'unlock'.
Do you know any friends who have a non EU sim you can try while in the UK, if not I can send you an Australian sim which is disconnected but will get the phone to ask you if you want to unlock the region lock.
Another option is to use software to perform the unlock, the video here is aimed and removing a normal sim lock but it can also remove region lock.
Thats the best bet, the other option is using a rooted phone (which invalidates warranty).
Failing that you could take the phone back to car phone warehouse, dont tell them you used the M1 sim first, and advise its a fault on the phone, and get them to give you a new phone place a 10 minute call and use the M1 sim in it before you leave the store.