There's a lot of people on XDA with UK phones who are having this issue and after trying a sim from Asia/USA etc, they report that the phone doesn't work.
Thus is an incredibly big issue for me and means that the phone is now completely off the table. What were Samsung thinking?
I was so stoked for this phone too
SIM restrictions on unlocked European Note3 - xda-developers
Edit: I'll continue to check though.