[Sony Ericsson Xperia Neo, Pro] ZduneX25:
Found it:

Phonebook.apk > res > layout > dialpad.xml

it loads text values (not images for digits), so I made text transparent and used own icons for normal and pressed buttons :)

<?xml version="1.0" encoding="utf-8"?>
<com.sonyericsson.android.socialphonebook.ButtonGridLayout android:id="@id/dialpad" android:layout_width="wrap_content" android:layout_height="wrap_content" android:directionality="none"
xmlns:android="http://schemas.android.com/apk/res/android">
<FrameLayout android:id="@id/one" android:background="@drawable/dial_num_1" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_1_txt" />
<ImageView android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_voicemail_margin_bottom" android:src="@drawable/dialpad_voicemail_icn" />
</FrameLayout>
<FrameLayout android:id="@id/two" android:background="@drawable/dial_num_2" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_2_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_2_txt" />
</FrameLayout>
<FrameLayout android:id="@id/three" android:background="@drawable/dial_num_3" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_3_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_3_txt" />
</FrameLayout>
<FrameLayout android:id="@id/four" android:background="@drawable/dial_num_4" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_4_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_4_txt" />
</FrameLayout>
<FrameLayout android:id="@id/five" android:background="@drawable/dial_num_5" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_5_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_5_txt" />
</FrameLayout>
<FrameLayout android:id="@id/six" android:background="@drawable/dial_num_6" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_6_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_6_txt" />
</FrameLayout>
<FrameLayout android:id="@id/seven" android:background="@drawable/dial_num_7" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_7_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_7_txt" />
</FrameLayout>
<FrameLayout android:id="@id/eight" android:background="@drawable/dial_num_8" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_8_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_8_txt" />
</FrameLayout>
<FrameLayout android:id="@id/nine" android:background="@drawable/dial_num_9" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_9_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Small.Secondary" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_label_text_size" android:layout_gravity="bottom|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_label_margin_bottom" android:text="@android:string/general_dialpad_label_9_txt" />
</FrameLayout>
<FrameLayout android:id="@id/star" android:background="@drawable/dial_num_star" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_star_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_star_button_num_text_margin_top" android:text="@android:string/general_dialpad_star_txt" />
</FrameLayout>
<FrameLayout android:id="@id/zero" android:background="@drawable/dial_num_0" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/lockscreen_strings_dialpad_0_txt" />
<TextView android:textAppearance="@android:style/SEMCTextAppearance.Medium.Secondary" android:textColor="#00000000" android:layout_gravity="bottom|center" android:paddingLeft="@dimen/dialpad_button_zero_label_padding_left" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/dialpad_button_zero_label_margin_bottom" android:text="@android:string/general_dialpad_label_0_txt" />
</FrameLayout>
<FrameLayout android:id="@id/pound" android:background="@drawable/dial_num_pound" android:focusable="true" android:clickable="true" android:layout_width="@dimen/dialpad_button_width" android:layout_height="@dimen/dialpad_button_height" android:soundEffectsEnabled="false" android:directionality="none">
<TextView android:textAppearance="@android:style/SEMCTextAppearance.ExtraLarge" android:textColor="#00000000" android:textSize="@dimen/dialpad_button_num_text_text_size" android:layout_gravity="top|center" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="@dimen/dialpad_button_num_text_margin_top" android:text="@android:string/general_dialpad_hash_txt" />
</FrameLayout>
</com.sonyericsson.android.socialphonebook.ButtonGridLayout>