I can't turn on my phone - Apple iPhone 6 Plus (iOS8)
Cause 7 of 10: Your phone is locked to another operator
If your phone is locked to another operator and you're trying to use a Vodafone SIM, the display will tell that your SIM is invalid.
Solution: Before you can use a Vodafone SIM, you need to unlock your phone using an unlock code. To get the unlock code, contact the operator that locked the phone.