Attribute Number: 20
  Value: String

  This attribute is used when a RADIUS implementation is set up to
  return a user's call. This is commonly used in corporate situations
  to avoid long-distance charges in hotel rooms and other remote
  locations. This value, A STRING, is often the identifier for a
  profile configured on the service equipment; there is no specific
  standrad for a string name, a triggered action, or something else.
  In other words, it is environment specific. RADIUS client gear is
  allowed to reject a connection if this attribute is present but
  not supported by the gear.