Contact.php

<?php

namespace Sk\CmsBundle\Entity;

class Contact 
{
   private $name;

   public function __construct(Contact\ContactName $name)
   {
       $this->name = $name->toString();
   }

   public function changeName(Contact\ContactName $name)
   {
      $currentName = new ContactName($this->name);

      if ($currentName->isDifferentFrom($name)) {
          $this->name = $name->toString();
      }
   }
}

ContactName.php

<?php

namespace Sk\CmsBundle\Entity\Contact;

class ContactName
{
    private $name;

    public function __construct($name)
    {
        if (false === $value || (empty($value) && '0' != $value)) {
            throw new \InvalidArgumentException('Cannot create contact with empty name');
        }

        $this->name = $name;
    }

    public function toString()
    {
        return $this->name;
    }

    public function isDifferentFrom(ContactName $name)
    {
        return $this->name !== $name->toString();
    }
}