GetCountryCode

Use compile 'com.googlecode.libphonenumber:libphonenumber:8.0.1' depencency. This makes task easy and provide accurate result because its by google https://github.com/googlei18n/libphonenumber

Then you can make your own Custom Adapter like I have made here:

public class CountryCodesAdapter extends BaseAdapter {

private final LayoutInflater mInflater;
private final List<CountryCode> mData;
private final int mViewId;
private final int mDropdownViewId;
private int mSelected;

public static final class CountryCode implements Comparable<String> {
    public String regionCode;
    public int countryCode;
    public String regionName;

    @Override
    public int compareTo(String another) {
        return regionCode != null && another != null ? regionCode.compareTo(another) : 1;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o)
            return true;

        if (o != null && o instanceof CountryCode) {
            CountryCode other = (CountryCode) o;

            return regionCode != null &&
                    regionCode.equals(other.regionCode);
        }

        return false;
    }

    @Override
    public String toString() {
        return regionCode;
    }
}

public CountryCodesAdapter(Context context, int viewId, int dropdownViewId) {
    this(context, new ArrayList<CountryCode>(), viewId, dropdownViewId);
}

public CountryCodesAdapter(Context context, List<CountryCode> data, int viewId, int dropdownViewId) {
    mInflater = LayoutInflater.from(context);
    mData = data;
    mViewId = viewId;
    mDropdownViewId = dropdownViewId;
}

public void add(CountryCode entry) {
    mData.add(entry);
}

public void add(String regionCode) {
    CountryCode cc = new CountryCode();
    cc.regionCode = regionCode;
    cc.countryCode = PhoneNumberUtil.getInstance().getCountryCodeForRegion(regionCode);
    cc.regionName = getRegionDisplayName(regionCode, Locale.getDefault());
    mData.add(cc);
}

public void clear() {
    mData.clear();
}

public void sort(Comparator<? super CountryCode> comparator) {
    Collections.sort(mData, comparator);
}

@Override
public int getCount() {
    return mData.size();
}

@Override
public Object getItem(int position) {
    return mData.get(position);
}

@Override
public long getItemId(int position) {
    CountryCode e = mData.get(position);
    return (e != null) ? e.countryCode : -1;
}

public int getPositionForId(CountryCode cc) {
    return cc != null ? mData.indexOf(cc) : -1;
}

public void setSelected(int position) {
    mSelected = position;
}

@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
    CheckedTextView textView;
    View view;
    if (convertView == null) {
        view = mInflater.inflate(mDropdownViewId, parent, false);
        textView = (CheckedTextView) view.findViewById(android.R.id.text1);
        view.setTag(textView);
    }
    else {
        view = convertView;
        textView = (CheckedTextView) view.getTag();
    }

    CountryCode e = mData.get(position);

    StringBuilder text = new StringBuilder(5)
            .append(e.regionName)
            .append(" (+")
            .append(e.countryCode)
            .append(')');

    textView.setText(text);
    textView.setChecked((mSelected == position));

    return view;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    TextView textView;
    View view;
    if (convertView == null) {
        view = mInflater.inflate(mViewId, parent, false);
        textView = (TextView) view.findViewById(android.R.id.text1);
        view.setTag(textView);
    }
    else {
        view = convertView;
        textView = (TextView) view.getTag();
    }

    CountryCode e = mData.get(position);

    StringBuilder text = new StringBuilder(3)
            .append('+')
            .append(e.countryCode)
            .append(" (")
            .append(e.regionName)
            .append(')');

    textView.setText(text);

    return view;
}

/** Returns the localized region name for the given region code. */
public String getRegionDisplayName(String regionCode, Locale language) {
    return (regionCode == null || regionCode.equals("ZZ") ||
            regionCode.equals(PhoneNumberUtil.REGION_CODE_FOR_NON_GEO_ENTITY))
            ? "" : new Locale("", regionCode).getDisplayCountry(language);
}
}

Then you can create the Activity where you want to display all country codes, I have made a layout like this:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical">
    <include layout="@layout/toolbar_simple"/>
    <ScrollView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:scrollbars="vertical" >

        <LinearLayout
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:gravity="center_horizontal"
            android:orientation="vertical"
            android:padding="18dip" >

            <Spinner android:id="@+id/phone_cc"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:spinnerMode="dialog"/>

            <EditText
                android:id="@+id/phone_number"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/hint_validation_number"
                android:inputType="phone" />

            <Button
                android:id="@+id/button_validate"
                android:layout_width="match_parent"
                android:layout_height="fill_parent"
                android:text="@string/button_validate" />

           </LinearLayout>

    </ScrollView>
</LinearLayout>

My java Activity code is:

import android.annotation.SuppressLint;
import android.content.Context;
import android.os.Bundle;
import android.telephony.TelephonyManager;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

import com.amitupadhyay.getcountrycode.CountryCodesAdapter.CountryCode;
import com.google.i18n.phonenumbers.PhoneNumberUtil;
import com.google.i18n.phonenumbers.Phonenumber;

import java.util.Comparator;
import java.util.HashSet;
import java.util.Locale;
import java.util.Set;

public class NumberValidation extends ToolbarActivity {

    private Spinner mCountryCode;
    private EditText mPhone;
    private Button mValidateButton;

    /**
     * Compatibility method for {@link PhoneNumberUtil#getSupportedRegions()}.
     * This was introduced because crappy Honeycomb has an old version of
     * libphonenumber, therefore Dalvik will insist on we using it.
     * In case getSupportedRegions doesn't exist, getSupportedCountries will be
     * used.
     */
    @SuppressWarnings("unchecked")
    private Set<String> getSupportedRegions(PhoneNumberUtil util) {
        try {
            return (Set<String>) util.getClass()
                    .getMethod("getSupportedRegions")
                    .invoke(util);
        }
        catch (NoSuchMethodException e) {
            try {
                return (Set<String>) util.getClass()
                        .getMethod("getSupportedCountries")
                        .invoke(util);
            }
            catch (Exception helpme) {
                // ignored
            }
        }
        catch (Exception e) {
            // ignored
        }
        return new HashSet<>();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.number_validation);
        setupToolbar(false);

        mCountryCode = (Spinner) findViewById(R.id.phone_cc);
        mPhone = (EditText) findViewById(R.id.phone_number);
        mValidateButton = (Button) findViewById(R.id.button_validate);

        // populate country codes
        final CountryCodesAdapter ccList = new CountryCodesAdapter(this,
                android.R.layout.simple_list_item_1,
                android.R.layout.simple_spinner_dropdown_item);
        PhoneNumberUtil util = PhoneNumberUtil.getInstance();
        Set<String> ccSet = getSupportedRegions(util);
        for (String cc : ccSet)
            ccList.add(cc);

        ccList.sort(new Comparator<CountryCodesAdapter.CountryCode>() {
            public int compare(CountryCodesAdapter.CountryCode lhs, CountryCodesAdapter.CountryCode rhs) {
                return lhs.regionName.compareTo(rhs.regionName);
            }
        });
        mCountryCode.setAdapter(ccList);
        mCountryCode.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                ccList.setSelected(position);
            }

            public void onNothingSelected(AdapterView<?> parent) {
                // TODO Auto-generated method stub
            }
        });

        // FIXME this doesn't consider creation because of configuration change
        Phonenumber.PhoneNumber myNum = getMyNumber(this);
        if (myNum != null) {
            CountryCode cc = new CountryCode();
            cc.regionCode = util.getRegionCodeForNumber(myNum);
            if (cc.regionCode == null)
                cc.regionCode = util.getRegionCodeForCountryCode(myNum.getCountryCode());
            mCountryCode.setSelection(ccList.getPositionForId(cc));
            mPhone.setText(String.valueOf(myNum.getNationalNumber()));
        }
        else {
            final TelephonyManager tm = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
            final String regionCode = tm.getSimCountryIso().toUpperCase(Locale.US);
            CountryCode cc = new CountryCode();
            cc.regionCode = regionCode;
            cc.countryCode = util.getCountryCodeForRegion(regionCode);
            mCountryCode.setSelection(ccList.getPositionForId(cc));
        }
    }

    /** Returns the (parsed) number stored in this device SIM card. */
    @SuppressLint("HardwareIds")
    public Phonenumber.PhoneNumber getMyNumber(Context context) {
        try {
            final TelephonyManager tm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
            final String regionCode = tm.getSimCountryIso().toUpperCase(Locale.US);
            return PhoneNumberUtil.getInstance().parse(tm.getLine1Number(), regionCode);
        }
        catch (Exception e) {
            return null;
        }
    }
}