Chosen Solution
Can I use a iphone 6s plus sim card reader on a 6plus?
No they are Variants. the sim contact points on the boards are a different widths. if you have no other option it is possible to botch a connection but far better to replace any part like for like. sim tray faults only occur from customer damage or corrosion. if the sim is not registering it is most likely a modem issue.
