gistfile1.php

<?php

class A {
    public function foo() {
        B::baz();
    }
}

class B {
    static public function baz() {
        static::bam();
    }
    static  public function bam() {
        print 'called bam';
    }
}

$a = new A;
$a->foo();

# PHP Fatal error:  Call to undefined method A::bam() in /Users/tobias/Desktop/foo.php on line 11