BTW leela next time you google another advice make sure the link actual has what the OP requested as there is no MT4G there. Now OP ill make it easy for you as you have few meths.
FREE(easy): If you go via TMobile for unlock code then you need to supply them with your device IMEI. However if don't meet their requirements then you will need to send them additional info proving you bought the device.
PAY(easy): You can get the unlock code and pay small money, there are tons of 3rd party vendors who does this.
ROOT(hard): Well what you want to do is Radio S=OFF PermROOT, this will unlock your device and give you total control its free and well depending on your skill maybe easy or hard.