Radiobutton with text above button

The @style/TabStyle is simply a style that is applied, you can ignore that. The @drawable/main_selector is a graphic that is toggled depending on the situation. You can read more about selectors here.

Example to get text on top:

<?xml version="1.0" encoding="utf-8"?>
<RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<RadioButton
    android:text="Text on top"
    android:button="@null"
    android:background="#f00"
    android:layout_weight="1"/>

<RadioButton 
    android:text="Text on top"
    android:button="@null"
    android:background="#0f0"
    android:layout_weight="1"/>
</RadioGroup>

Will give following result:

If you want the Text to appear above the button you can use following xml:

<?xml version="1.0" encoding="utf-8"?>
<RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<RadioButton
    android:text="Text on top"
    android:button="@null"
    android:drawableBottom="@android:drawable/btn_radio"
    android:gravity="center"
    android:layout_weight="1"/>

<RadioButton
    android:text="Text on top"
    android:button="@null"
    android:drawableBottom="@android:drawable/btn_radio"
    android:gravity="center"
    android:layout_weight="1"/>
</RadioGroup>

This will give following result:

To complement Warpzit great answer, you should use android:gravity="center_horizontal|bottom" and android:layout_height="match_parent" on the buttons, to align them.

Also there's no need to copy the radio button drawables from AOSP, use ?android:attr/listChoiceIndicatorSingle.

XML Layout

<RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/radioGroup1"
    android:layout_width="400dp"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="20dp" >

    <RadioButton
        android:id="@+id/radio0"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:button="@null"
        android:drawableBottom="?android:attr/listChoiceIndicatorSingle"
        android:gravity="center_horizontal|bottom"
        android:text="RadioButton" />

    <RadioButton
        android:id="@+id/radio1"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:button="@null"
        android:drawableBottom="?android:attr/listChoiceIndicatorSingle"
        android:gravity="center_horizontal|bottom"
        android:text="RadioButton dsfsdfsdfsdfsdf" />

    <RadioButton
        android:id="@+id/radio2"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:button="@null"
        android:drawableBottom="?android:attr/listChoiceIndicatorSingle"
        android:gravity="center_horizontal|bottom"
        android:text="RadioButton fdsfsd fdsfsdf fsfsdfs" />

</RadioGroup>