First check that the phone is not locked with a different network. If it is, then you need to unlock. To unlock, I suggest you can approach Prounlocking.com and specify the country,locked network of Samsung Galaxy Note 5.Based on the availability you can get the permanent unlock service along with free instructions. It uses a nano sim card. so get the appropriate sim size. Follow instructions from samsung.com/us/support/answer/ANS00043237/ to insert the sim card.