Nearly all mobile service providers lock their branded phones to their own network to offset the discounts they give to contracted customers. To open line a cell phone means to unlock the phone so it can connect to other mobile networks. Opening a cell phone line requires the unlock code that is unique to your phone.
Turn on your cell phone. Dial "*#06#" and press the send button. Write down the 15-digit International Mobile Equipment Identity (IMEI) number that shows up.
Contact your mobile service provider and ask for the unique unlock code to your cell phone. Provide them with the IMEI number and an e-mail address to send the unlock code and instructions to.
Follow the unlock code instructions when you receive the email. Carefully enter the unlock code when prompted and restart your cell phone.
Remove the old SIM card from your cell phone. Insert the SIM card for your new mobile network to begin using your open-lined cell phone.
Every mobile service provider has its own criteria for releasing the unlock code. If you do not meet those criteria, you can also buy the unlock code from an online retailer that specialises in providing cell phone unlock codes.
Depending on your cell phone brand, you may have a limited number of attempts to enter the unlock code. The unlock code dialogue box will let you know how many attempts you have left. If you exceed the number of allotted attempts to enter the correct unlock code, your cell phone will be permanently locked to its current mobile network. According to AT&T, the iPhone cannot be unlocked, even if you are out of contract.