Dial *#06# on your phone's keypad. The number will appear on the screen. Alternatively, check the sticker under the battery.
Samsung SGH-A107 IMEI Unlock Code Generator: The Complete Guide -Extra quality- samsung sgh a107 imei unlock code generator
The phone may automatically reboot. You can now insert a SIM card from any GSM carrier. Dial *#06# on your phone's keypad