iPhone carrier lock
Purchased iPhone from private party and I do not know what carrier this device is locked out of so I can request it to be unlocked. Does apple have a way to know what iPhone was assigned or made for which carrier?
iPhone 6s
If the SIM card you have works to send and receive calls, then either the phone is locked to that carrier or the phone was unlocked from the original carrier and now works with any SIM card. Are you having a problem with different SIM cards from different carriers?