Don't worry i will help you.If your phone displays "Invalid Sim" message on the screen,it is locked to network.You need to get it unlocked from current network lock to use other network sim card in it.To unlock it use unlock code from online sites.So you can unlock it immediately.Visit the site Simpleunlocking.com get unlock code and get free unlocking instructions from Mobileunlockguide.com and unlock it step by step.