assets/carrier_config_51021.xml

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<carrier_config_list>
    <carrier_config>
        <string-array name="non_roaming_operator_string_array" num="1">
            <item value="51001"/>
        </string-array>
    </carrier_config>
</carrier_config_list>