mymodule_module.php

<?php

class MyModule_Module extends Core_ModuleBase
{

	protected function createModuleInfo()
	{
		return new Core_ModuleInfo(
			'MyModule',
			'Whatever...',
			'Aaron Hodges'
		);
	}
	
	public function subscribeEvents()
	{
		Backend::$events->addEvent('shop:onExtendCustomerModel', $this, 'extend_customer_model');
	}
	
	public function extend_customer_model()
	{
		$customer->define_column('phone', 'Phone')->validation()>required('Please specify a phone number')->fn('trim');
	}
	
}