What does it mean when you say "Phone is Locked to"

On all of our product pages, you are required to provide to us the network carrier that the phone you have is locked to. This means the network carrier that the phone is originally from. When filling out the form on our product page, please ensure that you do not select the network carrier that you want to use the phone with. 

Remember, you are unlocking your phone and not your SIM card. This means that after you have unlocked your phone, you can use it with any GSM SIM card rather than locking it to another one.