You can't start up your phone - Vodafone Smart Tab 3 10
Cause 1 of 5: Your phone is network locked
If your phone is locked to Vodafone's network and you want to use a SIM from another operator, the display will tell you that your SIM is invalid.
Solution: To use a SIM from another operator, you need to unlock your phone using the unlock code which can be obtained from the Vodafone website. Please note that certain conditions must be met before you can obtain the unlock code.