how to unlock cell phones

Hi every body.
I am ,in fact, we are having problem unlocking locked phones in Eritrea.
Most people came with therir pohone locked and can not use them in eritrea.
If you have any idea on how i could do this.Or if you know any software to generate a code to unlock cell phones.

Use different SIMM card, then try. I belive prepaid simm card available in your place.