Required in order to use another network's SIM card on your Orange San Francisco / ZTE Blade / ZTE Libra U-V880
You can unlock the Orange San Francisco / ZTE Blade / ZTE Libra U-V880 for free. Once unlocked, you may use any SIM card or network on your phone.
With some custom ROMs, you do not need to unlock the phone in order to use another SIM or network.
If you are not asked to enter an unlock code, the phone is either unlocked already or you are using a custom ROM that already unlocks your phone or you are trying to unlock with another Orange SIM.
Thanks to Arr Too for the IMEI calculator.