PHP 5.3.17, Zend Engine v2.3.0, Xdebug v2.2.1で確認

<?php

class a
{
	function a1(){
		echo "a1";
	}

	static function a2(){
		echo "a2";
	}
	
	function a3(){
		echo "a3";
	}
}

class a_Ex extends a
{
	function a1_1(){
		echo "a_Ex1_1";
		parent::a1();   // Non-static method a::a1() should not be called statically
	}

	static function a1_2(){
		echo "a_Ex1_2";
		parent::a1();   // Non-static method a::a1() should not be called statically
	}

	function a2_1(){
		echo "a_Ex2_1";
		parent::a2();
	}

	static function a2_2(){
		echo "a_Ex2_2";
		parent::a2();
	}

	function a3(){
		echo "a_Ex3";
		parent::a3();   // Non-static method a::a3() should not be called statically
	}
}

a_Ex::a1();   // Non-static method a::a1() should not be called statically
a_Ex::a1_1(); // Non-static method a_Ex::a1_1() should not be called statically
a_Ex::a1_2();
a_Ex::a2();
a_Ex::a2_1(); // Non-static method a_Ex::a2_1() should not be called statically
a_Ex::a2_2();
a_Ex::a3();   // Non-static method a_Ex::a3() should not be called statically

?>