UPDATE. I finally cut my Philippines SMART micro sim to nano sim. Inserted it into my Verizon iphone 6+ with the "US GSM/VZW N61/N56" notation, and it works fine - no "invalid sim" messge. Put it in a Tmobile locked 6+ and the SMART sim comes up invalid sim as expected.
So, that iphone 6+ that has the limited Verizon N61/N56 policy seems to be OK with an international sim - it just says "no service." Carrier in Setting/About is noted as SMART.
Will update in two weeks when I am back in the Philippines to see if all is well. If not, I will three iphone 6+ ipods for sale....
does the model number of your phone begin with "SVC" ???? for example here is the one I have that is locked.... Model: SVC,IPHONE 6 PLUS,MM,16GB,GOLD,CI/AR