Andorid自身数据库中有很多默认的apn配置，如果要配置新的默认配置:

1、找到该文件：android-source/device/fsl/imx6/etc/apns-conf.xml

2、添加如下的格式的apn：

    <apn carrier="Thailand TRUE 3GNET"
         mcc="520"
         mnc="04"
         apn="internet"
         user="true"
         server=""
         password="true"
         mmsc=""
    />

3、因为RIL层在初始化拨号的时候会从sim卡中读取apn，然后把读出的apn和预先数据库中的apn对比，如果匹配就按照数据库的信息去拨号。

4、获取sim卡apn代码片段如下：

    /**
     * Based on the sim operator numeric, create a list for all possible
     * Data Connections and setup the preferredApn.
     */
    private void createAllApnList() {
        mAllApns = new ArrayList<ApnSetting>();
        String operator = mPhone.mIccRecords.getOperatorNumeric();
        if (operator != null) {
            String selection = "numeric = '" + operator + "'";
            // query only enabled apn.
            // carrier_enabled : 1 means enabled apn, 0 disabled apn.
            selection += " and carrier_enabled = 1";
            if (DBG) log("createAllApnList: selection=" + selection);

            Cursor cursor = mPhone.getContext().getContentResolver().query(
                    Telephony.Carriers.CONTENT_URI, null, selection, null, null);

            if (cursor != null) {
                if (cursor.getCount() > 0) {
                    mAllApns = createApnList(cursor);
                }
                cursor.close();
            }
        }

        if (mAllApns.isEmpty()) {
            if (DBG) log("createAllApnList: No APN found for carrier: " + operator);
            mPreferredApn = null;
            // TODO: What is the right behaviour?
            //notifyNoData(GsmDataConnection.FailCause.MISSING_UNKNOWN_APN);
        } else {
            mPreferredApn = getPreferredApn();
            if (mPreferredApn != null && !mPreferredApn.numeric.equals(operator)) {
                mPreferredApn = null;
                setPreferredApn(-1);
            }
            if (DBG) log("createAllApnList: mPreferredApn=" + mPreferredApn);
        }
        if (DBG) log("createAllApnList: X mAllApns=" + mAllApns);
    }