How can i unlock or decode my Huawei phone?

I have a Huawei phone, but this phone has been configured to use only one operator, the Mobile Telephone Network (MTN) Cameroon. The phone model is Huawei G1157, the Imei is 358145030557996, and the S/N is IH4CAC4031704780. I need a code that will make possible for me to use sim cards from other operators like Orange Cameroon. Please also tell me in detail how to enter the unloke code in my moblie handset. Thank you .